A senior adviser to Vladimir Putin has called the Ukranian president a "Nazi" as Ukraine signed an association with the European Union.
While mainly an economic deal to set up a free-trade zone between the EU and three former Soviet republics – Ukraine, Georgia and Moldova – the agreement has political and strategic ramifications, and it was former Ukrainian president Viktor Yanukovych's U-turn over signing it at the end of last year that led to his ousting in a popular revolt.
Sergei Glazyev, an adviser to Putin, told the BBC before the signing that "Europe is trying to push Ukraine to sign this agreement by force" and said Petro Poroshenko, the president, lacked the legitimacy to make the deal.
"They organised [a] military coup in Ukraine; they helped Nazis to come to power. This Nazi government is bombing the largest region in Ukraine." He said he "of course" believed the Ukrainian president was a Nazi.
The association deal – which Poroshenko signed in Brussels on Friday – does not guarantee eventual EU membership, but is seen both in the countries themselves and in Moscow as a major step westwards. It contains measures to synchronise economies with EU nations, as well as improve rule of law and human rights.
Poroshenko said as he arrived for the signing ceremony that the deal offered Ukraine a fresh start after years of political instability. "It is a historic day," he said, describing it as the most important day since independence from Moscow in 1991.
Russia has expended huge energy in its attempts to coerce Ukraine into joining its rival Eurasian Union, but is now resigned to losing its western neighbour to Europe, even if unrest in the east continues to give Moscow a voice in Ukrainian affairs.
A week-long ceasefire in eastern Ukraine ends at 10pm on Friday but has been broken numerous times. The region witnessed sporadic fighting throughout the day on Thursday, including a rebel attack on an irregular troops unit stationed in the heart of Donetsk.
Kiev and separatist commanders have set up a third round of indirect negotiations in Donetsk that could agree another extension.
In Donetsk, a pro-Russian separatist leader announced the freeing on Friday of four observers from the Organisation for the Security and Cooperation in Europe (OSCE) who had been kidnapped by rebels in east Ukraine on 26 May.
"They have been freed without conditions. They are a Dane, a Turk, a Swiss national and, I believe, an Estonian," said Alexander Borodai, the prime minister of the self-proclaimed Donetsk People's Republic, which has declared independence from the Kiev government after a disputed referendum.
He said they had been held by a rebel chief in the neighbouring restive region of Lugansk.
While welcoming the release, Mark Etherington of the OSCE mission in Ukraine said the security body was still very worried about the fate of the second team of observers held since 29 May in eastern Ukraine by the pro-Moscow separatists.
Rebel leaders claim that they do not control the actions of all the militias in their region fighting against the Ukrainian forces sent to curb the insurgency.