"The problem for Ukrainians is that we have four to seven weeks, depending on nature," said Hanno Pevkur. "After that, we will probably see a bit less movement."
Estonia's Defence Minister has warned the Ukrainian counteroffensive faces time pressure with winter looming.
At a press briefing in Tallinn, Hanno Pevkur said the window was narrowing for Ukraine as it continues its attempt to rout Russian troops in its east and south.
"The problem for Ukrainians is that we have four to seven weeks, depending on nature. After that, we will probably see a bit less movement because of the weather", he told reporters.
"Let's see how it goes. But we have to acknowledge that the weather plays a huge part in the counteroffensive."
"I truly hope that in these coming weeks, maybe up to two months, Ukrainians can progress... in order to consolidate their forces and also have successes on the battlefield", he added.
Furnished with billions of euros of Western equipment, Ukraine started its big military push against Russian forces in June. Its armed forces have encountered a tough fight, with Moscow having had several months to prepare and using the time to undertake the digging trenches and laying landmines extensively.
Progress has been slow and is likely to be slower still when fast approaching wet, muddy and freezing weather conditions make large troop and vehicle movements more difficult.
"In south Ukraine, the situation is definitely not easy. We've seen... that Ukraine has made some progress. But, nevertheless, more than 100,000 square kilometres are occupied [by Moscow's army]," said Hanno Pevkur.
"I've been in contact with Ukrainians and they also say it's extremely difficult," he said, adding that the existence of Russian minefields mean "pure handwork" by Kyiv's soldiers is needed to move forward.
The Secretary of Ukraine's National Security and Defence Council, Oleksiy Danilov, described Russia's minefields as "insane" in August - with as many as five mines per square metre.
Ukraine's army reportedly broke through Russia's first line of defence on the crucial southern front near Zaporizhzhia at the end of last month, after gritty attritional fighting.
The Estonian Defence Minister, who has served in his post since April 2023, urged countries around the world to continue supporting Kyiv, with weapons and financial backing.
"Looking at the future. I believe that they [Ukraine] can continue... [to] move forward. This is why also international help must be there, because at the end of the day... Ukraine is fighting for the free world."
"All the dictators in the world are looking very closely at how Putin is acting and what will be the success rate in Ukraine [sic]," he added. "We have to help Ukraine because they really must win this war."
Though the West has largely rallied behind Ukraine, promising to do whatever it takes to help it defeat Russia, some countries hold different views towards the conflict.
“If you take the global picture, then support for Ukraine’s and the West’s fight against Russia is not completely solid – by a long shot,” Paul Rogers, Professor of International Security at the University of Bradford told Euronews in March.
Estonia, a small Baltic country, has emerged as a staunch supporter of Ukraine, fearing an assertive Russia. It was once part of the USSR, but has largely embraced its future within the EU and NATO, though there is ambivalence among some sections of the population.