A group of pro-Russian armed men stormed the public offices of Crimean regional capital Simferopol, panicking the nascent coup government in Kiev.

Witnesses said they wore unmarked camouflage uniforms and carried rocket-propelled grenades, sniper rifles and other weapons.

They raised the Russian flag over the local parliament building.

The men did not immediately voice any demands and threw a flash grenade in response to a journalist's questions.

They wore black and orange ribbons, a Russian symbol of the victory in World War II and put up a sign reading "Crimea is Russia."

The move posed an immediate challenge to Ukraine's new rebel authorities as they sought to set up an interim government.

Self-styled acting president Oleksandr Turchynov condemned the takeover in Crimea as a "crime against the government of Ukraine."

And he warned that any move by Russian troops off of their base in Crimea "will be considered a military aggression."

"Unidentified people with automatic weapons, explosives and grenades have taken over the governmental buildings and the parliament building in the autonomous region of Crimea," he complained.

And he added: "I have given orders to the military to use all methods necessary to protect the citizens, punish the criminals and to free the buildings."

Meanwhile Russian news agencies reported that elected President Viktor Yanukovych was now staying in the Barvikha state sanatorium village just outside Moscow.

"I have to ask Russia to ensure my personal safety from extremists," Mr Yanukovych reportedly said.

He said he still considers himself president and sees the new Ukrainian authorities as illegitimate.

Shortly after, the same agencies quoted an unnamed Russian official saying that Mr Yanukovych's request for protection "was satisfied on the territory of Russia."

In Kiev, the rump parliament chose Arseniy Yatsenyuk as their new prime minister.

The 39-year-old, pushed by the US as the "guy who's got the economic experience," said Ukraine didn't want a fight with Russia, but insisted he wouldn't accept the secession of the southern Crimea.

But his past willingness to negotiate with Mr Yanukovych meant that the crowds in Independence Square booed his name.

Figures from the Maidan protest movement scooped a number of top jobs - top medic Oleh Musiy was given the health minister job despite having no political experience.

The more politically experienced members of the coup cabinet come from the Fatherland Party, meaning former president Yulia Tymoshenko will be likely to wield significant influence.