Putin Orders Check of Army Readiness near Ukraine Border, U.S. Says Any Military Move in Neighboring Country a 'Grave Mistake'

Russian President Vladimir Putin on Wednesday ordered a snap check of the battle-readiness of the armed forces in the west and center of the country, including the area bordering Ukraine, as U.S. Secretary of State John Kerry warned that any Russian military moves in Ukraine would be a "grave mistake."

"The commander-in-chief has set the task of checking the capability of the armed forces to deal with crisis situations posing a threat to the military security of the country," said Defense Minister Sergei Shoigu, quoted by the Interfax news agency.

The drill involves army, navy and airforce troops based in the western military district, a vast territory bordering Ukraine, Belarus, the Baltic states, Finland and the Arctic.

The previously unannounced move comes amid turmoil in Ukraine that toppled pro-Russian president Viktor Yanukovych and unleashed separatist sentiment in some largely Russian-speaking regions such as Crimea.

Putin ordered a similar check last year, however, and said at the time that such drills should become regular events.

The drill, which Shoigu said is to check the troops' effectiveness in "resolving crisis situations threatening military security and also anti-terrorist (operations)," will run from Wednesday to March 3.

The last such check was carried out in July last year, involving more than 80,000 troops in far eastern Russia. It was the largest such snap check since the breakup of the Soviet Union in 1991.

Meanwhile, a man died of a heart attack also on Wednesday as pro-Russian demonstrators brawled with supporters of Ukraine's new interim authorities in the capital of the Russophone Crimea peninsula, as the local government ruled out debating a split from Kiev.

Scuffles erupted in Simferopol as thousands of pro-Moscow residents and Muslim Crimean Tatars backing the new leadership in Kiev held competing rallies outside the regional parliament, amid fears that Ukraine's pro-Moscow east could push for partition following the weekend ousting of Kremlin-backed Yanukovych.

Crimea's health ministry said that an unknown elderly man was found dead at the scene "without any traces of bodily injuries".

"According to initial information from medics, the cause of death was acute cardiac arrest," the ministry said.

An Agence France Presse journalist said that the two sets of demonstrators sprayed each other with pepper spray and used batons as police struggled to keep them apart during the brief fighting.

Ambulances were called as several people could be seen nursing light injuries before crowds dispersed following appeals from local lawmakers for them to go home.

Meanwhile the head of the parliament of the autonomous region -- where Russia's Black Sea fleet has been based for some 200 years -- rejected demands to discuss breaking away from the rest of Ukraine at an emergency session Wednesday, dismissing the idea as a "provocation".

"The question of leaving Ukraine will not be put before the parliament of Crimea," parliament speaker Volodymir Konstantinov said.

Shoigu announced later in the day that Russia is taking measures to ensure the security of its Black Sea naval fleet based on Ukraine's Crimean peninsula.

"We are watching carefully what is happening in the Crimea, what is happening around the Black Sea fleet. We are taking measures to ensure security of sites, infrastructure and arsenals of the Black Sea fleet," Shoigu said, RIA Novosti news agency reported.

Up until 1954, Crimea belonged to Russia but it was then given to the Ukrainian Soviet republic by USSR leader Nikita Khrushchev and has long been seen as a potential source of conflict.

Also on Wednesday, Arseniy Yatsenyuk, one of those who led the protests that rocked Ukraine, was picked to head up the government of the crisis-hit country until presidential elections are held in May.

The pro-EU former foreign minister's nomination was announced in front of tens of thousands of people on Kiev's Independence Square, the epicenter of three months of protest that culminated in the ouster of Yanukovych, along with an entirely new cabinet.

Yatsenyuk's nomination as prime minister still has to be approved by parliament, but it was greeted by cheers on the square, which just a week ago was at the heart of bloody clashes between protesters and security forces that left nearly 100 dead.

He now faces the tough task of dragging the ex-Soviet state back from the brink of collapse as Ukraine stands on the verge of default and faces separatist tensions.

Other key members of the new cabinet included Andriy Parubiy, the highly respected commander of the so-called Euromaidan protest movement, who was named head of the national security and defense council.

Dmytro Yarosh, the head of the controversial far-right paramilitary group Pravy Sektor that was a key component of the protests and whose members were often at the frontline of clashes, was offered the post of Parubiy's deputy but had not yet given his answer.

Dmytro Bulatov, meanwhile, the activist who was abducted and severely tortured in January and sent to Lithuania for treatment, became youth and sports minister.

Ukraine's interim leader Oleksandr Turchynov on Tuesday warned against "dangerous signs of separatism" after some 10,000 pro-Russian protesters took to the main square of the Crimean port town of Sevastopol over the weekend.

Western countries have warned the Kremlin not to meddle with Ukraine's territorial integrity and Russian Foreign Minister Sergei Lavrov toned down the rhetoric from Moscow on Tuesday by saying it was sticking to a policy of "non-interference".

The avalanche of change in the deeply divided former Soviet state came after scores of demonstrators were killed in Kiev last week when three months of anti-Yanukovych protests exploded into violence.

The demonstrations were sparked in November by Yanukovych's decision to spurn a historic pact with the EU in favor of closer ties with old master Russia, and grew into a titanic diplomatic tug-of-war over Ukraine's future direction.