Taoiseach Micheál Martin has said that Russia's war on Ukraine had turned the international order upside down.
He was speaking in Helsinki where he held discussions with both the President and Prime Minister of Finland.
Mr Martin also said the expulsion of two Irish diplomats from Moscow was "completely unjustified".
Also today, Finland said it would expel two Russian diplomats over the war in Ukraine.
It shares a 1,340-kilometre land border with Russia, and is currently considering whether to join NATO.
"The measure is in line with those taken by other EU member states", the prime minister's office said in a statement.
"In addition, the visa extension of one Russian embassy staff member has been cancelled."
The decision follows a cyber attack on Finland's government website and those of several ministries at the same time that Ukrainian President Volodymyr Zelensky gave a video address to the Finnish Parliament.
Earlier, Finland's ministry of defence reported a violation of Finnish airspace by a Russian state aircraft.
The Taoiseach said Russia was using forced migration of people fleeing war in the hope that EU states will buckle.
It was, he said, necessary to stand up to this type of "naked aggression" and the challenge for the EU is to put humanity first and to protect lives.
Addressing the media after meeting Finland's Prime Minister Sanna Marin, he said Ireland would at a later point reflect on the security implications of what he termed Putin's war.
Mr Martin warned of the threat of further cyber and hybrid attacks, saying the country will in the future have to reflect and talk to other States as well.
Echoing those fears, the Finnish prime minister said her country would conclude a careful discussion about joining NATO by mid-summer.
Sanna Marin said the country cannot take a long time to make this major decision given the severe security concerns arising from the war in Ukraine.
Taoiseach meets Finnish President pic.twitter.com/qM6bM35yOV
— Mícheál Lehane (@MichealLehane) April 8, 2022
Mr Martin has now travelled to Estonia for a bilateral meeting with Prime Minister Kaja Kallas.
He said they discussed impact of the war in Ukraine on security, defence, energy and the humanitarian crisis.
"We agreed that Putin and his regime must know it will not, and cannot, succeed."
While in Tallinn, the Taoiseach will visit the Cooperative Cyber Defence Centre of Excellence, which plays an important role in enhancing Europe's capacity to deal with cyber threats.
Finland and Estonia are two nations closely aligned with Ireland on issues around climate change, digital transformation, and perhaps most pertinently in their opposition to Russia's war on Ukraine.
