Explosions and warning sirens have been heard this morning in some of Ukraine's major cities after Russia's president ordered a "military operation" into the eastern part of the country.
Vladimir Putin claims his orders will "protect people" in breakaway regions - who he says have been subject to bullying and genocide and he's warned other nations not to intervene.
The Ukrainian president's advised people to stay home as much as possible.
The Russian president made the announcement in a TV address.
The US President's released a statement in response the latest developments.
Joe Biden says the prayers of the entire world are with the people of Ukraine as they suffer an unprovoked and unjustified attack by Russian military forces.
He added that President Putin has chosen a 'premeditated war that will bring a catastrophic loss of life and human suffering' and says the west will respond in a united and decisive way to 'hold Russia accountable'.
EU leaders will meet in Brussels this evening for an emergency summit over the Ukraine crisis.
Last night the Taoiseach told his parliamentary party what we're witnessing now's like nothing seen since World War 2.
European Affairs Minister, Thomas Byrne, says today's summit of EU leaders is hugely important.