Russia's Putin announces military operation in Ukraine

Russian President Vladimir Putin announced a military operation in Ukraine on Thursday with explosions heard soon after in the capital and other parts of the country, prompting outrage from Joe Biden who warned of a "catastrophic loss of life".

Weeks of intense diplomacy to avert war and the imposition of Western sanctions on Russia failed to deter Putin, who had massed between 150,000 and 200,000 troops along the borders of Ukraine.

"I have made the decision of a military operation," Putin said in a surprise television announcement shortly before 6:00am (0300 GMT) in Moscow.

He also called on Ukrainian soldiers to lay down their arms, and  justified the invasion by claiming a "genocide" in Ukraine's east.

The Kremlin had earlier said rebel leaders in eastern Ukraine had asked Moscow for military help against Kyiv. 

A reporter in Kyiv, Ukraine's capital, heard explosions within about 30 minutes of Putin's announcement. Explosions were also heard in the eastern city of Mariupol and the Black Sea port of Odessa, according to reporters.

US President Biden immediately warned of "consequences" for Russia and said the world would "hold Russia accountable" for its actions.

He said Russia's move would cause "catastrophic loss of life and human suffering", while NATO's chief condemned Russia's Reckless and unprovoked attack on Ukraine.

At the United Nations, Ukraine called on the world body "to do everything possible to stop the war".

Ukraine's President Volodymyr Zelensky had made an emotional appeal late on Wednesday night to Russians not to support a "major war in Europe".

Speaking Russian, Zelensky said that the people of Russia were being lied to about Ukraine.

Zelensky said he had tried to call Putin but there was "no answer, only silence", adding that Moscow now had around 200,000 soldiers near Ukraine's borders.