A senior adviser to Russian President Vladimir Putin has lashed out at Ukraine's president ahead of the signing of a controversial EU deal.Sergei Glazyev said Petro Poroshenko was a "Nazi" and his endorsement of the deal was "illegitimate".Mr Poroshenko is expected to sign the full association agreement at the EU summit in Brussels later.A shaky ceasefire in eastern Ukraine, where pro-Russian rebels are fighting government forces, is also due to end.In another development early on Friday, rebels released four international observers captured more than a month ago.Alexander Borodai, head of the self-styled Donetsk People's Republic, said the members of the Vienna-based Organisation for the Security and Co-operation in Europe (OSCE) had been freed as a goodwill gesture."We don't expect anything in return - we freed them without any pre-conditions," he said.The OSCE said it remains concerned about four other observers captured at about the same time.Mr Glazyev, Mr Putin's presidential adviser on regional economic integration, told the BBC: "Europe is trying to push Ukraine to sign this agreement by force."They organised [a] military coup in Ukraine, they helped Nazis to come to power. This Nazi government is bombing the largest region in Ukraine."Asked if he believed Mr Poroshenko was a Nazi he replied: "Of course."Mr Poroshenko's predecessor, Viktor Yanukovych, was overthrown in February after refusing to sign the EU deal under pressure from Russia.Russia went on annex Ukraine's Crimea region and pro-Russia separatists in eastern regions declared independence, claiming that extremists had taken power in Kiev.Political parts of the association agreement, aiming at forging closer ties with the EU, were signed by Ukraine's interim government in March.Mr Poroshenko previously announced he would sign the crucial trade and economic relations portion of the pact on Friday.Mr Glazyev added: "I think after the signing of the agreement with EU, [the] European public will be... surprised when this Nazi Frankenstein, which was born by the Euro bureaucrats and some politicians, will knock on the European countries' doors."He said Mr Poroshenko was an "illegitimate" president because parts of Ukraine did not vote in May's elections.His claims come despite President Putin engaging with the Ukrainian leader on peace negotiations.Fighting is said to have continued in some areas of eastern Ukraine despite a temporary ceasefire this week.Talks on extending the truce in in the Donetsk and Luhansk regions are also set to take place on Friday.More than 420 people have been killed in fighting between pro-Russia rebels and government forces in eastern Ukraine since mid-April, the UN estimates.Russia denies it has allowed militants and heavy weaponry to cross its border into eastern Ukraine.The US and EU are threatening to impose further sanctions if Russia does not act to defuse the situation.(BBC)Bakudaily.az