The Taoiseach has warned the United Nations the world is at risk of a new nuclear arms race.
Leo Varadkar criticised Russia for threatening to use nuclear armaments in its conflict with Ukraine if there is an escalation from the West.
He also said the international community had failed when it comes to Israel and Palestine.
Speaking in New York on Friday night, Mr Varadkar told the UN Ukraine deserves the unqualified support of all member states.
"Ireland has long been committed to building a world free of nuclear threats, but we see a world in which their place in security doctrines is growing rather than diminishing.
"This must be reversed. The stark alternative is a new nuclear arms race... that must not pass."
Mr Varadkar called the war in Ukraine an "imperialist and brutal invasion" and condemned Russia for ending the Black Sea grain export deal.
“This is about right and wrong. This is 2023 and no country should try to change borders by force and no country should try to bring down a democratic government by military means or by supporting a military coup. There cannot be equivocation on this.
“It was an act of unprovoked and unjustified aggression by an expansionist, revanchist power against its neighbour.
“The brutality of Russia’s actions in Ukraine has caused unfathomable suffering for the people of that country.”
He said every country in the UN had a “deep interest in ensuring that Russia did not succeed in its attempt to move borders by force – and that this was not just a European problem.
“For when one aggressor prevails, their peers elsewhere take note and are emboldened. We know this from history.
“When Europeans draw attention to the profound injustice of what is happening in Ukraine, there can be criticism, some of it justified, of the developed world’s failure to respond with the same intensity of feeling and action to conflict and suffering elsewhere.
“But, while we can acknowledge that we have fallen short, the people of Ukraine should not be the ones asked to pay the price.
“They have done nothing to bring down this war on their heads.”