Ukraine's new Western-backed leaders on Thursday blamed Russian agents and the ousted pro-Kremlin president for organizing two days of carnage in Kiev that killed nearly 90 supporters of closer EU ties.

The explosive allegation were leveled only moments after Russia lashed out at NATO for building up the defenses of ex-Soviet nations and brandished the threat of further hikes in the price Ukraine must pay for gas after ousting its Kremlin-backed leaders.

Latvia has asked the head of the Russian Orthodox church, Patriarch Kirill, to postpone a planned visit amid tension between Russia and the Baltic states over Moscow's actions in Ukraine.

A letter from Latvian President Andris Berzins requesting that the May visit be put off indefinitely was handed to Kirill's representatives in Moscow on Thursday.

Russian troops deployed close to the Ukrainian border will return to base after completing their exercises, Foreign Minister Sergei Lavrov said Thursday.

"After finishing training in the Rostov region (bordering Ukraine), one of the battalions that took part has already returned to base in the Samara region."

NATO warned on Wednesday that Russia's military presence on the flashpoint border with Ukraine was of "grave concern" and that Moscow's forces could reach military objectives in just days.

General Philip Breedlove, NATO's top commander, told the Wall Street Journal that Russian troops could invade vast portions of Ukrainian territory in three days to five days.

Deposed Ukrainian president Viktor Yanukovych said on Wednesday he did not approve of Crimea leaving Ukraine, but blamed the new authorities in Kiev for the region's annexation by Russia.

"If this had happened under me, I would have tried not to let it happen," he said in an interview with Russian television, calling the events in Crimea "a pain and a tragedy that is very hard to agree with".

Crimea's Tatars are considering the possibility of a vote on increased autonomy, a local leader has said, a move likely to deepen the crisis on the Russian-controlled peninsula.

The minority group's assembly, known as the Mejlis, has created a special group to look into the possibility of holding a "referendum within one ethnic group", said its leader Refat Chubarov in a statement released late on Tuesday.

Crisis-hit Ukraine took the first step Wednesday toward granting more powers to the regions in line with Western wishes but stopped well short of creating the federation sought by Russia.

The announcement came as Russia continued to mass tens thousands of troops along Ukraine's eastern border following a vow by President Vladimir Putin to use "any means necessary" to protect the interest of his compatriots in the neighboring ex-Soviet state.

Syrian President Bashar Assad said Wednesday that key ally Moscow had helped re-establish "a multipolar world", as he met with a high-level Russian delegation in Damascus.

The delegation was delivering a message from Russian President Vladimir Putin, who has provided political, military and financial backing to Assad's regime since the outbreak of a revolt in March 2011.

Russia on Wednesday accused NATO of succumbing to "Cold War" instincts after the alliance suspended all cooperation with Moscow over the Crimea crisis.

"Basic instincts of Cold War have awoken in NATO, affecting rhetoric accordingly," the official Twitter page of Russia's mission to NATO quoted envoy Alexander Grushko as saying.

Moscow on Wednesday threatened retaliatory action against U.S. diplomats after U.S. bank JP Morgan blocked a transfer of funds carried out by a Russian envoy.

Russia considered as "unacceptable, illegal and absurd the decision of JP Morgan Chase bank to block the transfer by the Russian ambassador in Astana to insurance company Sogaz," said Alexander Lukashevich, a spokesman for the Russian foreign ministry.