President Michael D Higgins has said there is "no room anymore for anyone to avert their gaze" from Gaza.
His comments come after an Israeli airstrike on a school in Gaza city that had been used to house people displaced by the war.
The attack on the compound housing displaced families killed around 100 people, the Hamas-run Gaza government said, while the Israeli military said it had targeted Hamas militants and cast doubt on the Palestinian death toll.
President Higgins said that airstrike will be "condemned by all those seeking to find peace in what is a continuing horrific violation of human rights".
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"The comments made by the High Representative of the EU for Foreign Affairs, Josep Borrell, that there is no justification for the massacres which have taken place following the targeting of at least 10 schools in recent weeks must be taken with the utmost seriousness by all Member States," he added.
"Practical measures of a diplomatic kind are now urgently needed to ensure there is no further extension of the loss of life and total devastation of infrastructure in the region.
There is no room anymore for anyone to avert their gaze. The outrageous level of killing must end with an immediate ceasefire, the release of all hostages, and the immediate provision of all necessary aid."
Tánaiste and Minister for Foreign Affairs Micheál Martin has reiterated calls for a ceasefire in the Middle East after the attack.
"I condemn the airstrike by Israel on a school in Gaza, with reports of dozens of civilian deaths. An immediate ceasefire and the release of all hostages is a priority," Mr Martin said in a social media post.
"It's time for the slaughter to stop," he added.
