A number of airlines have grounded flights as Ukraine's president has declared martial law and the country's foreign minister says a "full-scale invasion" has begun.
Explosions have been heard and seen in the Ukrainian capital of Kyiv and other major cities following Vladimir Putin's announcement that a military operation was underway.
The sound of distant blasts were picked up in a live broadcast from US outlet CNN, causing reporter Matthew Chance to put on a flak jacket.
