Russian President Vladimir Putin heads to China on Tuesday to shore up eastern ties as relations with the West plunge to new lows over the Ukraine crisis.

During a two-day visit to Shanghai, Putin and Chinese host Xi Jinping will seek to clinch a raft of agreements including a landmark gas deal crucial for Moscow as Europe seeks to cut reliance on Russian oil and gas.

Leaders of Crimea's Tatar community on Saturday called off a ceremony to commemorate 70 years since their deportation by Stalin, after an official ban and fears of unrest.

Tensions have risen between local authorities and the Tatars -- Turkic-speaking Muslims who make up about 12 percent of Crimea's population -- since Russia's annexation of the Ukrainian peninsula in March.

Hungarian Prime Minister Viktor Orban on Friday renewed a controversial call for autonomy for his ethnic kin in western Ukraine, less than a week after sparking a diplomatic row with both Kiev and Warsaw.

"The full weight of the Hungarian state is behind the autonomy demands of the Transcarpathian Hungarians," Orban said in an interview on the M1 public television channel late Friday.

Presidents Barack Obama and Francois Hollande warned Russia on Friday of significant new sanctions if Moscow keeps up its "provocative and destabilizing" behavior in Ukraine.

During their telephone call, the U.S. and French leaders also discussed the hunt for more than 200 kidnapped schoolgirls in Nigeria and a conference Hollande is hosting in Paris this weekend on combating the Islamic militant group Boko Haram that is holding them, the White House said in a statement.

U.S. Secretary of State John Kerry on Friday denounced fresh human rights abuses of Crimea's Tatars, 70 years after the minority group was expelled from the then-Soviet Union.

The Tatars, a Turkic-speaking Muslim group, will commemorate the anniversary of the mass deportation on Sunday amid tensions over Moscow's annexation of the peninsula, which has revived memories of the tragedy.

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.

Hungary asked Brussels on Thursday to lift the immunity of an MEP from the far-right Jobbik party, amid reports he was being investigated on allegations of spying for Russia.

"Hungary's chief prosecutor Peter Polt has turned to European Parliament President Martin Schulz to suspend the parliamentary rights of MEP Bela Kovacs," Polt's spokesman Geza Fazekas told Agence France Presse.

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.