The Ukrainian armed forces still need supplies of equipment and weapons to avoid heavy losses, says President Zelenskyy.
The Ukrainian troops' counteroffensive is delayed indefinitely as, according to Ukrainian President Volodymyr Zelenskyy, "more time is needed."
The president stressed members of new brigades were fully ready, with some units having received training abroad. But the Ukrainian armed forces still need supplies of equipment and weapons to avoid heavy losses.
What is Kyiv waiting for?
Since the end of last year, there has been talk of a large-scale Ukrainian counteroffensive. For security reasons, Kyiv stopped short of announcing specific dates, but experts in the West have previously suggested the start of the operation could take place any time from the end of April to the first two weeks of June.
"I think the reason why he announced it now is that expectations for this counteroffensive have quite clearly got out of hand in many circles," says Simon Schlegel, a senior Ukraine Analyst at the International Crisis Group. "Anticipation has been very, very high. And the reason for that is probably because there is a narrative going around, especially in Russia, that Ukraine only has 'one punch one try' at this very complicated counteroffensive. And therefore, it's probably a good thing right now that from the very top, that Zelenskyy himself, tries to also tone down expectations a bit."
The Ukrainian president says his armed forces need more equipment. On 9th May, US Secretary of State Antony Blinken said Kyiv already had everything it needed for the operation, including equipment and soldiers trained in the West, and stressed it was up to the armed forces command to draw up a plan for success.
Some experts believe the delay is because Kyiv wants to be as sure as possible of the success of any counteroffensive.
"In this situation, you cannot have enough. Simply put, it's always better to have more especially ammunition," says Schlegel. And both sides have been running quite low. It's become not just a military supply issue, but an industrial issue, a production issue. And it's possible that ammunition is currently the bottleneck that Zelenskyy wants to widen before actually risking the lives of his soldiers."
Max Bergmann, Director of the Europe, Russia and Eurasia Program at the Center for Strategic & International Studies agrees.
"We know the Ukrainians have obtained a number of tanks and they've obtained a number of other armoured personnel carriers and transport vehicles," he explains. "But I'm sure they're still waiting for more deliveries. So the question for Ukraine is, do you wait and wait for more deliveries to arrive but potentially give Russia more time to prepare for the potential counteroffensive?"
However, some Western observers believe the Ukrainian president's statement is calculated to dupe Moscow into believing the counteroffensive has been delayed - when in fact it has already begun.
Dr Neil Melvin, Director of International Security Studies at the Royal United Services Institute (RUSI) says it's important to understand what the word 'counteroffensive' actually means:
"I think often the images are kind of a shock and awe moment where all of the tanks roll forward. But actually, the counteroffensive itself is a long term process," he says. "And I would argue that, in fact, the counteroffensive by Ukraine has already started. What they're trying to do is shape the battlefield at the moment and they're pulling the Russian forces in different directions. They're trying to find gaps by probing and they're moving their forces around."
What kind of weapons does Ukraine need?
According to Bloomberg, since December (i.e. in preparation for a perceived counteroffensive) Ukraine has received the equivalent of $30bn of Western equipment and supplies - more than the annual military budget of any NATO country (except the US). For the entire period, the amount of aid has exceeded $67bn.
Kyiv is now talking about the need for long-range weapons, aviation and air defence systems.
On 11 May, London announced it was sending Storm Shadow tactical missiles with an estimated range of 560 km to Kiev (however, the export versions are limited to 250 km). According to experts, this is not simply just another weapons delivery, but one that could play an important role in the upcoming operation.
Melvin explains why these weapons are a potential game changer.
"Actually what they do is strike at Russia's ability to coordinate its own defence, so what we saw earlier in the war where the United States provided Ukraine with HIMARS artillery, that was very damaging to the Russians because with this artillery the Ukrainians could destroy logistical hubs at headquarters," he explains. "The Russians have adapted. They've pushed those facilities out of range of HIMARS. With these new missiles, suddenly they're back in range."
What some believe the success or failure of a Ukrainian counteroffensive boils down to is the ability of the Ukrainian armed forces to coordinate as accurately and quickly as possible between different units and government agencies.
"What Ukraine has to do is what's called combined arms warfare which means linking the air force, the ground forces, the intelligence community, the political leadership and keeping in contact with this very complicated set of actors as the armed forces move forward," Melvin continues. "So it's not just about breaking through the Russian lines, but actually sustaining that."
But there are difficulties ahead. Storm Shadow missiles are airborne and can be launched from a range of European-made aircraft - Tornado, Typhoon, Mirage 2000 and Rafale.
According to available information, Ukraine does not yet have these planes. In February, British Prime Minister Rishi Sunak said the transfer of Typhoons to Kyiv was not impossible, and it was even reported that training of Ukrainian pilots had begun.
The Ukrainian air force already has experience of using Western missiles from Soviet aircraft. Many of these machines, adapted to NATO standards, were supplied to Ukraine by the former Warsaw Pact countries.
However, Kyiv is demanding modern Western-made fighter jets - first and foremost, the American F-16s.
According to experts, these planes simply will not make it before the spring-summer campaign and it will take too much time to train Ukrainian pilots and adapt the country's airfield and technical infrastructure.
Secondly, it's unlikely they would play a significant offensive role in the war, as Bergmann outlines:
"We have to realise that Russia's advanced fighter jets and other aircraft are not operating to the same degree as expected in this war because of Ukraine's air defences. Russia also has substantial air defence capabilities, which would pose a threat to any Western fighters that Ukraine obtains.
"I think it's essential that Ukraine receives fighter jets. It's an additional form of air defence which can be used to protect Ukrainian skies, both from missiles, drones and Russian fighter jets. But here, it appears they will play more of a defensive rather than offensive role."
Before the full-scale invasion, the West believed that Kyiv would hold out for days or at best weeks because of the superiority of the Russian air force. But as early as 5 March, after just 10 days of war, Moscow reported that Ukraine's air force and air defences had been suppressed and destroyed.
This was not the case. Ukraine's air and air defence forces not only retained combat effectiveness but ultimately prevented Russia from gaining air superiority.
However, any Ukrainian counteroffensive will also face a number of other serious obstacles.
According to experts, for the first time in modern history, countries of an equal technical level have faced each other on the battlefield. Moreover, both Russia and Ukraine built their air defence system on Soviet principles. During the Cold War, the USSR created a large number of very different, ground-based air defence systems. Together they were supposed to create a theoretically impenetrable multi-levelled barrier at all altitudes and speeds. This means the Soviet pilot training school focused more on operating against a "Western" system than its own.
As a result, air defence activity at high altitudes has forced aircraft on both sides to switch to operations at ultra-low altitudes, literally just a few metres above the ground. But there, for a variety of reasons, it has proved more effective to use drones.
Will the counteroffensive prove decisive?
Many Western political analysts have not ruled out the possibility that the failure of a Ukrainian counteroffensive could lead to a reduction in Western assistance - simply because it has almost exhausted its ability to supply equipment and gear without compromising its own security. This would put pressure on Kyiv to reach a ceasefire on the terms of the status quo.
"I think there are other aspects beyond military success that will influence how supportive Western audiences and Western governments will be in the next phase. How well Ukraine manages to reintegrate the territories they liberate. Will this create a refugee crisis, for example, in Crimea? How they treat prisoners of war, and how well they manage the dangers of escalation. I think these factors are almost as important as a pure military success that is measured in liberated territory," Schlegel adds.
But now, alongside the readiness of Ukraine's armed forces for a counter-offensive, there are increasing calls for long-term, strategic support for the country. Even if the armed forces fail to achieve the goals of the spring and summer campaign, the West is being called on not abandon its support for Kyiv.
Back in March, EU leaders began to seriously consider increasing the production of weapons and ammunition - especially for Ukraine.
"While it's right to focus on the counteroffensive and making sure Ukraine has everything, I think there also needs to be a political message," says Melvin. "In most scenarios, the counteroffensive will not end the war by the summer. So the Western community needs now to factor in that this war is going to be a long war and that Ukraine is going to need resources to continue to fight to bring it to an end. But even beyond that, even if Russia is defeated in Ukraine, Russia is likely to remain a major threat to Ukraine, but also to the wider Europe."