Five topless activists from the Femen feminist group protested in New York's Times Square on Thursday to denounce Russia's incursion into Ukraine, asking for tougher U.S. and EU action against Moscow.

The women, whose bare chests were painted blue and yellow -- the color of Ukraine's flag -- hoisted a placard slamming Russian President Vladimir Putin's "occupation" of Crimea and another urging, "U.S.-EU, stop talking start acting".

Russian President Vladimir Putin is seeking to profit to the maximum from Ukraine's turmoil by implementing the de-facto annexation of Crimea at high speed to wrong foot an indecisive West, analysts said.

The ousting of the generally pro-Russian Ukrainian president Viktor Yanukovych was a major defeat for Putin and means that the ex-Soviet state is now swiftly aligning itself with the European Union in a historic switch away from the Kremlin.

Ukrainian police on Thursday arrested scores of pro-Moscow militants including a self-declared "people's governor" in the eastern city of Donetsk after re-taking regional government headquarters.

Officers from Ukraine's security services notified Pavel Gubarev of the arrest order against him at his home in Donetsk.

A referendum in Crimea on joining Russia announced for this month was welcomed by many in the peninsula Wednesday but looks set to hamper Western hopes of keeping Ukraine together.

While some Crimea residents would see rejoining Russia as a return to the region's rightful status, experts say the vote on March 16 could draw out the military stand-off and make it very hard to broker a diplomatic solution.

A U.S. guided-missile destroyer is en route to the Black Sea but naval officials said Thursday it was a "routine" deployment that was planned before the crisis unfolded in Ukraine.

The USS Truxtun departed the Greek port of Souda Bay Thursday to carry out joint training with Romanian and Bulgarian forces, the U.S. Navy said in a statement.

Russian soldiers may not be in Yalta, but locals are worried about their tourist season as the city on Crimea's Black Sea coast wakes up to the first spring sun amid fears of a possible war between Ukraine and Russia.

In the seaside city nestled in the foothills of the Ukrainian Riviera, police loyal to the authorities in Kiev patrol the seafront with their hands in their pockets.

Stepping up pressure on Russia, the United States on Thursday slapped visa bans on those Russians and Ukrainians it blames for destabilizing Ukraine and set the stage for more sanctions.

The White House said President Barack Obama was ordering visa bans "in response to Russia's ongoing violation of Ukraine's sovereignty and territorial integrity."

Syria's President Bashar Assad has expressed his "solidarity" with Russian President Vladimir Putin's position on the crisis in Ukraine, state media reported on Thursday.

In a telegram, Assad "expressed... Syria's solidarity with Putin's efforts to restore security and stability to Ukraine in the face of attempted coups against legitimacy and democracy in favor of radical terrorists", state news agency SANA said.

Pro-Moscow authorities in Crimea on Thursday asked Russian President Vladimir Putin to examine a request for their region to join the Russian Federation, which will be put to a referendum on March 16.

"The parliament of Crimea has adopted a motion for Crimea to join Russia. It has asked the Russian president and parliament to consider this request," Grigoriy Ioffe, a senior lawmaker, told AFP.

The United States will on Thursday send six additional F-15 fighter jets to step up NATO's air patrols over the Baltic states, mission host Lithuania said as West-Russia tensions simmered over Ukraine.

"I have had confirmation that the air police missions will be reinforced by six additional F-15 fighters," Defense Minister Juozas Olekas told AFP.