KIEV - President Vladimir Putin put 150,000 Russian combat troops on high alert for war games near Ukraine on Wednesday, the Kremlin’s boldest gesture yet after days of sabre rattling since its ally Viktor Yanukovich was toppled as president in Kiev.

Moscow denied that the previously unannounced drill in the western military district near Ukraine was linked to events in its neighbour but it came amid a series of increasingly strident statements about the fate of Russian citizens and interests.

With the political turmoil hammering Ukraine’s economy, the central bank said it would no longer intervene to shield the hryvnia currency, which tumbled 4 percent on Wednesday and is now down a fifth since January 1. Wednesday’s abrupt abandonment of Ukraine’s currency peg sent ripples to Russia where the rouble fell to five-year lows and bank shares fell.

Thousands of ethnic Russians, who form the majority in Ukraine’s Crimea region, demonstrated for independence. They scuffled with rival demonstrators supporting the new Kiev authorities. The Crimea is home to part of Russia’s Black Sea Fleet, which Moscow said it was taking steps to secure.

One person died in the Crimea protest, apparently of a heart attack during a crush of the crowd, Interfax news agency reported. A Reuters correspondent on the scene reported surging crowds and scuffles but no major violence.

NATO defence ministers, meeting in Brussels, issued a statement supporting "Ukrainian sovereignty and independence, territorial integrity, democratic development, and the principle of inviolability of frontiers”. Their statement made no direct mention of the Russian war games.

U.S. Secretary of State John Kerry said Russia should respect the territorial integrity of Ukraine and be "very careful” in its judgments toward its neighbour.

"What we need now to do is not get into an old, Cold War confrontation,” he said on MSNBC television.

Russia’s foreign ministry said Ukrainian extremists were "imposing their will”, and a Ukrainian church affiliated with the Moscow-based Russian Orthodox Church had faced threats.

Earlier Moscow denounced the rise of "nationalist and neo-fascist sentiment” in Ukraine’s mainly Ukrainian-speaking west and said Russian speakers were being deprived of rights.

It has repeatedly expressed concern for the safety of Russian citizens in Ukraine, using language similar to statements that preceded its invasion of Georgia in 2008.

"In accordance with an order from the president of the Russian Federation, forces of the Western Military District were put on alert at 10.00 GMT today,” Interfax news agency quoted Russian Defence Minister Sergei Shoigu as saying.

Shoigu also said Russia was also "carefully watching what is happening in Crimea” and taking "measures to guarantee the safety of facilities, infrastructure and arsenals of the Black Sea Fleet,” in remarks reported by state news agency RIA.

Since Yanukovich’s downfall on Friday, all eyes have been on Putin, who ordered the invasion of neighbouring Georgia in 2008 to protect two self-declared independent regions with many ethnic Russians and others holding Russian passports, and then recognised the regions as independent states.

Any military action in Ukraine, a country of 46 million people that has close ties with European powers and the United States, would be far more serious - the closest the West and Russia have come to outright confrontation since the Cold War.

Despite the alarm raised by the sabre-rattling, many analysts expect Putin will pull back before taking armed action.

Agencies