The ministry said on Wednesday a senior Irish army officer had called Israeli military liasion officers at least six times to warn them that Israeli munitions were landing close to UN installations in the region.
The peacekeepers were killed on Tuesday night when an aerial bomb struck a United Nations Interim Force in Lebanon (UNIFIL) building in Khiam, southern Lebanon, an UNIFIL spokesman said.
"On six separate occasions he [the officer] was in contact with the Israelis to warn them that their bombardment was endangering the lives of UN staff in South Lebanon," a department of foreign affairs spokesman said.
The dead were Canadian, Finnish, Austrian and Chinese nationals.
Kofi Annan, the United Nations secretary general, has condemned Israel, saying he was shocked by the "apparently deliberate targeting" of the post, and calling for it to investigate the incident.
Several international governments and organisations also expressed their anger at the bombing.
Ehud Olmert, the Israeli prime minister, expressed "deep regrets" earlier on Wednesday over the deaths in a telephone conversation with Annan, his office said, but the Israeli premier said it was "inconceivable" for the UN to think that the incident was deliberate.
Dan Gillerman, the Israeli ambassador to the UN, also said that Annan's comments were "premature and erroneous" for implying that Israel had deliberately targeted the observers.
The US government on Wednesday defended Israel, saying that although the attack was "horrible" there was no indication that the post had been targeted.
Since clashes between Israel and Hezbollah fighters began two weeks ago, there have been several incidents of firing close to UN peacekeepers and observers, including direct hits on nine positions, a UN official told the Associated Press news agency.
UNIFIL has almost 2,000 peacekeepers and has been deployed in the southern Lebanon for almost 30 years, mainly providing protection and humanitarian assistance to the local population.