Ukraine is drawing up plans to withdraw its soldiers and their families from Crimea, Kiev's security chief says.

Andriy Parubiy said they wanted to move them "quickly and efficiently" to mainland Ukraine.

Earlier, pro-Russian forces seized two naval bases - including Ukraine navy's HQ - in Crimea. Kiev says its navy chief has been detained.

It comes a day after Crimean leaders signed a treaty with Moscow absorbing the peninsula into Russia.

A referendum in Crimea on Sunday, approving its split from Ukraine, came nearly a month after Kiev's pro-Russian President Viktor Yanukovych was replaced by Western-leaning interim authorities.

Nato Secretary General Anders Fogh Rasmussen has called the crisis in Crimea "the gravest threat to European security and stability since the end of the Cold War".

There were charged exchanges in a session of the UN Security Council, during which US envoy Samantha Power said her Russian counterpart Vitaly Churkin "showed more imagination than Tolstoy or Chekhov".

"Russia it seems has re-written its borders but it cannot rewrite the facts," said Ms Power, who was then accused by Mr Churkin of dropping "to the level of the tabloid press".

(BBC)