Iran is urging the UN Security Council to stop Israel threatening military action against its nuclear programme.
Iran and Israel are the bitterest of foes in a conflict-riven region
The highly unusual request was sent by Iran's UN envoy Mohammad Khazaee, to Secretary General Ban Ki-moon.
Mr Khazaee said Israeli threats were unacceptable and unjustifiable, and flagrantly violated international law.
Israel's UN envoy called the letter "disgusting dangerous... hypocrisy" in the light of what Iranian leaders have said about Israel.
Ambassador Dan Gillerman said the secretary general should not even reply to Mr Khazaee's letter.
Mr Khazaee stressed that Iran's nuclear programme was for peaceful purposes only, and said the UN should respond to Israeli threats of force by unambiguously condemning them.
The diplomatic spat in New York between the old Middle East foes came late on Wednesday.
Earlier in the day, Iranian President Mahmoud Ahmadinejad reportedly launched a new strongly worded attack against Israel, describing it as a "dirty microbe", and a "savage animal".
"For a country whose leader describes a member state of the United Nations [in such terms], to complain about others' statements is the height of hypocrisy," Mr Gillerman said.
"It is a letter which the recipients, be it the Security Council or the secretary-general, should not even honour by acknowledging," he added.
There have been press reports that Israel, which bombed an Iraqi reactor in 1981, has begun planning for a possible raid against Iran.
The Israeli government says it has not ruled out the possibility of using military force if Iran does not scrap its controversial uranium-enrichment programme.