NATO chief Anders Fogh Rasmussen said Friday he could no longer trust Russia's assurances on the territorial integrity of countries in the region after its annexation of Crimea.

"After what we have seen in Ukraine, no one can trust Russia's so-called guarantees on other countries' sovereignty and territorial integrity," Rasmussen told a press conference during a visit to Romania.

The United Nations warned Friday of an "alarming deterioration" of human rights in eastern Ukraine, where the government is battling an insurgency by armed pro-Russian separatists.

In a new report, U.N. High Commissioner for Human Rights Navi Pillay also voiced deep concern about "serious problems" of harassment and intimidation facing the Tatar community in Crimea, which was annexed by Russia in March in the face of international outrage.

U.S. Secretary of State John Kerry reiterated Washington's opposition to France's sale of warships to Russia during a meeting with French counterpart Laurent Fabius earlier this week, U.S. officials said Thursday.

Under a 1.2-billion-euro ($1.6 billion) deal agreed in 2011, France is to sell two Mistral-class helicopter carriers to Russia, despite criticism from several allies.

Only a third of voters in the Russian-speaking east of Ukraine plan to turn out for this month's crunch presidential election, according to an opinion poll published Thursday.

The survey, conducted nationwide ahead of the May 25 vote, also found that billionaire chocolate tycoon Petro Poroshenko was the clear front-runner for the post.

President Vladimir Putin said Thursday that Russia is "still open" to talks on Ukraine's gas debt, accusing the EU of failing to make specific proposals to help prevent a cutoff of supplies from next month.

In an open letter to European leaders, Putin also called on Brussels to "more actively engage" in finding ways to stabilize crisis-hit Ukraine's economy.

Just 10 days before a key presidential election, Ukraine's interim leaders were battling Thursday to keep the country together despite a European peace push, facing a bloody insurrection in the east and a tense standoff with Russia.

Kiev on Wednesday hosted the first round of so-called national unity talks under an OSCE initiative to try to resolve the deepening crisis on Europe's eastern flank and allow the May 25 vote to go ahead.

Pro-Russia protesters disrupted a public meeting with German Chancellor Angela Merkel in Berlin Wednesday, calling for the arrest of "Nazis" in Ukraine.

Around a hundred protesters, wearing caps emblazoned with the Russian two-headed eagle emblem, booed the chancellor and brandished placards bearing slogans such as "Arrest the Nazis in Ukraine" and "No war against Russia".

A university in Venice on Wednesday said Russian Culture Minister Vladimir Medinsky had cancelled a planned visit to collect an award following a protest by students and professors over his nationalist views.

"The minister cancelled his visit. The ceremony has been postponed indefinitely," said Federica Scotellaro, a spokeswoman for Ca' Foscari University.

Ukraine's embattled leaders launched round-table talks Wednesday as part of a Western-backed push to prevent the country falling apart, vowing they would not bow to "blackmail" by pro-Russian rebels waging an insurgency in the east.

The so-called national unity discussions -- which crucially do not involve the insurgents -- are being held barely two weeks before Ukraine holds a presidential election that the West is scrambling to keep alive.

Ukraine launches Western-sponsored roundtable "national unity" talks on Wednesday but without pro-Moscow rebels who are waging an armed insurgency in the east that threatens to tear the country apart.

The discussions open a day after rebels killed seven Ukrainian soldiers in an ambush, the deadliest single loss of life for the military since it launched an offensive against the separatists in April.