The Department of Foreign Affairs has urged Irish citizens in the Ukraine to seek shelter.
Russia launched a "full-scale invasion" of Ukraine overnight, with President Vladimir Putin warning: "To anyone who would consider interfering from the outside: if you do, you will face consequences greater than any you have faced in history. All relevant decisions have been taken. I hope you hear me."
Any Irish citizen in Ukraine has been urged to look for shelter, as explosions and gunfire are heard across the country.
Taoiseach Micheal Martin has "utterly condemned" the overnight stealth invasion of Ukraine by Vladimir Putin's Russian troops.
The world woke up to the shocking news that a military assault had begun overnight, with bombings of the Capital, Kyiv, continuing this morning.
The Taoiseach said this morning: "I utterly condemn Russia’s indefensible attack on the sovereign people of Ukraine.
"Our first thoughts are with them. We will work with the EU and UN to hold Putin and his regime accountable. Russia will pay a high price for this outrageous act of aggression. We stand with Ukraine."
Meanwhile, the Minister for Foreign Affairs and Minister for Defence Simon Coveney has hit out at Russia's invasion of Ukraine in a strong statement.
Speaking on Morning Ireland on Thursday morning, Mr Coveney said: "We are in complete solidarity with Ukraine. This is an illegal act of aggression from Russia. They are lying about the justification for it.
"It's an attack on Ukraine and an attack on the kind of Europe that we, collectively, have built since World War Two.
"You will see the EU working with other countries to take a strong stance now. The emergency leaders meeting will bring much tougher sanctions, I believe. It will send a very clear signal: We cannot accept this."
Mr Coveney added that there had been multiple attempts to negotiate with President Putin in the build up to this week's events, but these had been to no avail.
He noted: "Russia has decided to ignore all that and proceed with what seems to have been planned for a long time. We are not going to go to war with Russia, militarily. Sanctions will be tough, and the EU will suffer from counter-sanctions.
"What President Putin has done and said is not only to start a war with Ukraine with a broad invasion, he has also warned and threatened any country that intervenes. We are seeing a language that we haven't seen in many decades in Europe of aggression and brutality.
"This is a moment when the European Union needs to act together. We need extraordinary unity. Yes, Ireland is a neutral country militarily, but we are not neutral on this, when there is blatant aggression on the continent."
Meanwhile, Irish citizens have been warned to seek shelter in the country.
The Department of Foreign Affairs said in a statement: "The Department of Foreign Affairs recommends that all Irish citizens currently in Ukraine seek shelter in a secure place. We advise that citizens do not move around the country in the coming hours and to follow the advice of local authorities. The Department of Foreign Affairs advises against all travel to Ukraine.
"The Department will issue regular updates via press release and on the @dfatirl Twitter account as the situation develops."
Mr Coveney had earlier tweeted: "Russia has launched a full scale invasion of Ukraine. God help them. Rocket attacks & explosions across the country. Make no mistake: this is a shocking murderous act of aggression against a sovereign peaceful state. EU and world needs to respond strongly.
"Our thoughts & prayers are with the innocent people of Ukraine, as families wake up to shocking Russian attacks. Russian leaders are lying to their own people to justify this illegal aggression. We utterly condemn Russia for this act of unjustifiable war in the heart of Europe."
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