Ireland's embassy in Kyiv has ceased operating.
The ambassador and other staff have been moved to a secure location as fighting continues in Ukraine.
A dedicated helpline has been set up for Irish citizens in the country on 01 613 1700.
Foreign Affairs Minister Simon Coveney said Europe will respond to Russian aggression together.
"I've been in politics for 25 years, I'm not sure that I have ever seen anything that has united the EU in the way that this issue is currently uniting European countries, countries that have very different relationships with Russia historically."
Ireland will back the “strongest possible and most comprehensive” package of sanctions against Russia to punish the country for its invasion of Ukraine, the Taoiseach has said.
Micheál Martin said the punitive measures will reflect the “grave nature” of the assault on the Ukrainian people.
Speaking ahead of the summit of EU leaders, Mr Martin said he will support sanctions in the financial, energy and transport sector that would help “weaken the industrial base of Russia” and its capacity to wage a war.
EU leaders are meeting on Thursday evening to discuss and agree on a range on sanctions against Moscow.
It’s not a situation that we wanted to be in, but we are coming here this evening and I coming here representing Ireland, along with my European colleagues to, in the first instance, collectively condemn the outrageous and immoral attack on the territorial integrity of Ukraine and on its people,” Mr Martin said.