Russian President Vladimir Putin has announced a military operation in Ukraine, with explosions heard soon after across the country and its foreign minister warning a “full-scale invasion” was under way.

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

Putin called on Ukrainian soldiers to lay down their arms and said the operation was overseeing a “genocide” in the east of Ukraine.

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

The extent of Thursday’s attacks was not immediately clear, but Ukraine Foreign Minister Dmytro Kuleba said the worst-case scenario was playing out.

Biden immediately warned of “consequences” for Russia and that there would be a “catastrophic loss of life and human suffering”.

NATO’s chief condemned Russia’s “reckless and unprovoked attack” on Ukraine.