Russia attacks Ukraine: Footage shows military vehicles cross from Crimea, border guards say

Russian troops launched a wide-ranging attack on Ukraine on Thursday, as President Vladimir Putin cast aside international condemnation and sanctions and warned other countries that any attempt to interfere would lead to 'consequences you have never seen.'

Ukrainian border guards released footage of what they said were Russian military vehicles moving in, and big explosions were heard in the capital Kyiv, Kharkiv in the east and Odesa in the west. As the Russian military claimed to have wiped out Ukraine's entire air defences in a matter of hours, Ukrainians fled some cities and European authorities declared Ukrainian air space an active conflict zone.

World leaders decried the start of a long-anticipated invasion with far-reaching consequences, as global financial markets plunged and oil prices soared. Russia's actions could cause massive casualties, topple Ukraine's democratically elected government and upend geopolitics and Europe's post-Cold War security balance.

Governments from the U.S. to Asia and Europe readied new sanctions after weeks of failed efforts for a diplomatic solution -- but global powers have said they will not intervene militarily to defend Ukraine.

Ukrainian President Volodymyr Zelenskyy declared martial law, saying Russia has targeted Ukraine's military infrastructure. Ukrainians who had long braced for the prospect of an assault were urged to stay home and not to panic even as Ukrainian authorities reported artillery barrages and airstrikes on targets around the country.