Ireland is not one bit neutral when it comes to assassination bids and chemical attacks, the Taoiseach said as he justified the decision to expel a Russian diplomat.
Leo Varadkar rejected claims from Sinn Fein that the move against Moscow in response to the nerve agent attack in Salisbury undermined Ireland's long-standing military neutrality.
Sinn Fein leader Mary Lou McDonald said Mr Varadkar was taking the decision based on the intelligence assessment of the UK.
"Essentially Taoiseach you are asking us to trust Boris Johnson (UK foreign secretary) and dare I say it this might not be the wisest course of action," she told the Taoiseach during exchanges in the Dail parliament.
Mr Varadkar said the expulsion of the Russian diplomat was a show of solidarity with the UK.
He insisted Ireland had "no quarrel with the Russian people".
The Taoiseach noted that other neutral countries, such as Sweden and Finland, has also expelled diplomats in response to the Salisbury incident.
"Ireland is a neutral country, we do not join military alliances, we will not be joining Nato, we will not be part of a European army," he said.
"However, when it comes to terrorism, assassinations and the use of chemical weapons and cyber terrorism we are not neutral, one bit."
Earlier, Ireland's deputy premier Simon Coveney described the Salisbury attack as an affront to international law and order.
Former Russian intelligence officer Sergei Skripal and his daughter Yulia remain critically ill in hospital following the March 4 attack, which has been widely blamed on Russia.
Tanaiste and foreign affairs minister Mr Coveney announced the expulsion after briefing cabinet colleagues at Government Buildings on Tuesday morning.
"The use of chemical weapons, including the use of any toxic chemicals as weapons, by anyone, anywhere, is particularly shocking and abhorrent," he said.
"The attack in Salisbury was not just an attack against the United Kingdom, but an affront to the international rules-based system on which we all depend for our security and well-being.
"In light of the European Council conclusions, and following an assessment conducted by the security services and relevant departments, I have briefed the Government on my intended course of action.
"The Secretary General of the Department of Foreign Affairs and Trade has subsequently met with the Ambassador of the Russian Federation and informed him that the accreditation of a member of his staff with diplomatic status is to be terminated, in line with the provisions of the Vienna Convention on Diplomatic Relations.
"The individual in question is required to leave the jurisdiction."
Russia has 17 accredited diplomats working out of the Russian embassy in Rathgar in south Dublin.
Ahead of an anticipated expulsion announcement, Russia's ambassador to Ireland, Yury Filatov, had warned against any action that might "ruin" the relationship between the two countries.
"We should be concerned about the best interest of the Irish public and best interest of the Russian public, the Irish/Russian relations," he told RTE on Monday night.
"We have a huge amount of goodwill, we have a very nice relationship, positive, constructive, stable relations, open dialogue and good business.
"I don't see anything which would really point to the necessity to ruin it."