The UN Secretary General visited Russia for talks on Tuesday, meeting with Foreign Minister Sergei Lavrov and President Vladimir Putin.
The visit came as Kyiv's mayor, Vitali Klitschko, made a plea for more Western weapons, and Russia's state-owned Gazprom said it would cut off gas supplies to Poland and Bulgaria.
Meanwhile, Russian attacks continued against targets in Ukraine, with the US defence secretary saying that he believes Ukraine can still win the fight.
Read our blog below to see how events unfolded on Tuesday 26 April:
Tuesday's key points:
British PM Boris Johnson has rejected a Russian allegation that NATO is fighting a 'proxy war' in Ukraine.
Russia's state-owned Gazprom says it will cut off gas supplies to Poland and Bulgaria because they refuse to pay in rubles.
Kyiv Mayor Vitali Klitschko has made a plea for more Western weapons.
President Putin says he hopes there will be a "positive result" for talks between Russia and Ukraine, citing progress at recent talks in Istanbul.
UN Secretary-General Antonio Guterres used a visit to Moscow to call for an independent investigation into possible war crimes. Guterres said "I am concerned about the repeated reports of violations of international humanitarian and human rights law and possible war crimes."
US Defence Secretary Lloyd Austin says he believes Ukraine can win the war, after talks with allies in Germany.
Russia has threatened the UK with a "proportional response," following comments by the British defence secretary that it would be acceptable for Ukrainian forces to attack military targets on Russian soil.
Germany set to authorise the delivery of "Cheetah" type tanks to Ukraine , a major turning point in the cautious approach Berlin has taken to sending military supplies to Ukraine.
That's our live blog closing for Tuesday, thanks for reading today.
We're back early on Wednesday morning with the latest developments.
Boris Johnson rejects Russia's 'NATO proxy war' allegations
British Prime Minister Boris Johnson says his country does not want war “to escalate beyond Ukraine’s borders,” and rejected an allegation by Moscow that the West is fighting a proxy conflict with Russia.
But Johnson said Ukrainians “are being attacked from within Russian territory” and “have a right to protect and defend themselves” by striking inside Russia.
Russian Foreign Minister Sergey Lavrov has accused NATO of “pouring oil on the fire” with its support for Ukraine, and said the risk of World War III should not be underestimated. Russia has singled Britain out for criticism after a UK government minister said it was legitimate for Ukraine to hit fuel depots in Russia with UK-supplied weapons.
In an interview with British station Talk TV, Johnson said “it’s very, very important that we don’t accept the way that the Russians are trying to frame what is happening in Ukraine.”
He said: “They are trying to frame this as a conflict between Russia and the West, or Russia and NATO. That’s not what is going on.”
Russia's Gazprom stops deliveries to Poland and Bulgaria
The Bulgarian government says Russia's Gazprom will suspend its gas deliveries from Wednesday, citing Bulgarias refusal to comply with the supplier's new requirements.
Following the introduction of sanctions against Russia for its invasion of Ukraine, the Kremlin warned EU countries that their gas supply would be cut off if they did not pay in rubles.
Western countries refused to do so, saying they could continue to pay in euros or dollars.
Gazprom will also stop delivering gas to Poland from Wednesday, Polish gas company PGNiG said Tuesday evening.
"All deliveries to customers are made according to their request," assured the Polish company.
The Polish government has also said it is ready to deal with any supply disruptions from Russia, with Climate Minister Anna Moskwa writing on Twitter "there will be no shortage of gas in Polish homes."
Poland's PM Mateusz Morawiecki said gas storage facilities were 76% full and Poland was ready to "get gas from all other possible sources".
Zelenskyy: 'Russia put the world on brink of catastrophe' in Chernobyl
Ukrainian President Volodymyr Zelenskyy on Tuesday accused Russia of having put the world "on the brink of catastrophe" by occupying the Chernobyl power plant at the start of its invasion of Ukraine.
"The world was once again on the brink of catastrophe" Zelenskyy told reporters at a joint press conference with the head of the International Atomic Energy Agency IAEA in Kyiv.
"For the Russian army the Chernobyl zone and the Chernobyl plant were like normal territory for the conduct of military operations" Zelenskyy said.
Vladimir Putin 'still believes in a positive outcome' of Ukraine war
Russian President Vladimir Putin told UN chief Antonio Guterres on Tuesday that he still believed in a positive outcome to negotiations with Ukraine, despite the ongoing fighting between the two countries.
"I hope that we will reach a positive result," he said during his meeting with Guterres in the Kremlin.
He said the negotiations between Moscow and Kyiv in Istanbul at the end of March had achieved "a serious breakthrough because our Ukrainian colleagues had not linked the requirements of security, of Ukraine's international security, to some understanding of Ukraine's internationally recognised borders".
During those talks, Kyiv had proposed an international agreement establishing countries that would guarantee its security.
In exchange, Ukraine would accept a "non-nuclear" and neutral status, renounce NATO membership, and agree not to host foreign military bases on its territory -- and exclude issues about Crimea and Donbas from the negotiating table for the time being.
After those initial Istanbul talks, Moscow redeployed its troops from northern Ukraine near the capital Kyiv, to positions in the east of the country instead.
However, the negotiations were severely hampered by the discovery of numerous bodies in Ukrainian areas occupied by the Russian army before its withdrawal, notably in the town of Bucha. Ukraine accuses Moscow of killing civilians, which the Kremlin strongly denies.
Mr Putin said on Tuesday that the Russian army had "no connection" with the "provocation" in Bucha.
During his meeting with the Russian leader, Antonio Guterres reiterated his call for the UN and Moscow to work together to establish humanitarian corridors and help civilians in Ukraine.
In a statement, the UN said Vladimir Putin had agreed "in principle" to the involvement of the UN and the International Committee of the Red Cross in the evacuation of civilians trapped at the Azovstal industrial site in the besieged Ukrainian port of Mariupol.
According to the source, discussions will continue between the UN Office for the Coordination of Humanitarian Affairs and the Russian Defence Ministry.
US Defence Secretary: 'Ukraine war has already weakened Russian military'
The US Defence Secretary Lloyd Austin says the war in Ukraine has already weakened Russia's military capability.
Austin said after meeting allies and partners at the United States’ Ramstein Air Base in Germany on Tuesday that, since Russia began the invasion, its land forces have sustained “pretty substantial” casualties, as well as lost a lot of equipment and used a lot of precision-guided munitions.
He said that “they are, in fact, in terms of military capability, weaker than when they started, and … it’ll be harder for them to replace some of this capability as they go forward because of the sanctions and the trade restrictions that have been placed on them.”
Austin reiterated that “we would like to make sure, again, that they don’t have the same type of capability to bully their neighbors that we saw at the outset of this conflict.”
He criticised Russian Foreign Minister Sergey Lavrov’s warning that the threat of a nuclear conflict “should not be underestimated.”
Austin said that “it’s unhelpful and dangerous to rattle sabers and speculate about the use of nuclear weapons.”
Ukraine 'resolutely supports' Moldova, says Ukrainian FM
The Ukrainian Foreign Ministry has said that it “resolutely supports Moldova’s territorial integrity," following a series of explosions in the country's Moscow-backed separatist region of Trans-Dniester.
In a statement released on Tuesday, it said: Ukraine “resolutely supports Moldova’s territorial integrity within its internationally recognized borders and condemns attempts to draw the Trans-Dniester region of Moldova into the full-fledged war unleashed by Russia against Ukraine.
"[Ukraine] call[s] for deescalating tensions,” it added.
The ministry described Tuesday and Monday's attacks on an administrative building in Tiraspol, the centre of the separatist Trans-Dniester province of Moldova, along with explosions that hit broadcast antennas and other facilities in the region, as concerning.
Their statement follows a Russian officer’s comments about Moscow’s intention to fully take control of Ukraine’s south and build a land corridor to Trans-Dniester.