Here are the latest developments in the conflict between Russia and Ukraine:
Russian President Vladimir Putin appears on television to announce a military operation in Ukraine to defend separatists in the east of the country against "genocide" shortly before 6 am (0300 GMT).
Explosions ring out before dawn in Ukraine's capital Kyiv and several cities near the frontline and along the country's coast.
Ukraine's Foreign Minister Dmytro Kuleba accuses Putin of launching a "full-scale invasion".
Russia's ground forces cross into Ukraine from several directions, Ukraine's border guard service says.
Ukraine's President Volodymyr Zelensky declares martial law and later breaks diplomatic ties with Russia.
The head of the Ukrainian military says he has received orders from Zelensky to repel a Russian invasion and to "inflict maximum losses".
Russia's defence ministry says it has neutralised Ukrainian military airbases and its air defence systems.
Ukraine says it has killed "around 50 Russian occupiers" while repulsing an attack on a town on the frontline with Moscow-backed rebels.
Belarus leader Alexander Lukashenko says that his military is not taking part in the invasion, as Kyiv says Russian troops were entering the country from Belarusian territory.
US President Joe Biden says the "world will hold Russia accountable" over the military onslaught that he warned will cause a "catastrophic loss of life".
Poland asks NATO to activate Article 4, which calls for emergency consultations if a member is threatened.
Oil prices soar past $100 for the first time in more than seven years after Putin announces the invasion.
Moscow and Saint Petersburg stock exchanges say they are "suspending" trading.
Russia closes shipping in the Azov Sea, which lies between Russia and Ukraine.
China calls for restraint on all sides and says it is "closely watching" the latest situation.
Amid emotional scenes at the UN Security Council, Ukrainian ambassador Sergiy Kyslytsya trades barbs with his Russian counterpart, telling him, "There is no purgatory for war criminals. They go straight to Hell, ambassador."
Ukraine closes its airspace to civilian travel "due to the high risk to safety."
Flights from cities in southern Russia near Ukraine are cancelled.