The European Union and Russia have joined condemnation of the Iranian president's public call for Israel to be "wiped off the map".
Mr Ahmadinejad warned Muslim leaders not to recognise Israel
Mahmoud Ahmadinejad's remark has already been condemned by individual EU states and Canada who all summoned Iranian diplomats for an explanation.
A top Israeli minister called for Iran to be expelled from the United Nations.
The White House said the comment showed the US was right to be concerned about Iran's nuclear programme.
Western governments are bound to see the remark as further proof that Iran's hardline president is disinclined to curb his country's controversial nuclear programme, says the BBC's diplomatic correspondent, Bridget Kendall.
They may hope that a co-ordinated diplomatic protest will help step up the pressure, she adds.
"Those who insist on transferring the Iranian nuclear dossier to the UN Security Council have received an additional argument for doing so," Russian Foreign Minister Sergei Lavrov said during a trip to Jordan.
"What I saw on television was unacceptable," added the minister, whose country has been supplying civilian nuclear know-how to Iran, and he promised Moscow would bring its concern to Iran's attention.
An International Atomic Energy Agency (IAEA) report last month said questions about Iran's nuclear programme remained unanswered despite an intensive investigation.
The UK, France, Germany and the US are pressing Iran to provide more access to its nuclear plans.
EU leaders meeting in London issued a joint condemnation "in the strongest terms" following statements of concern from individual members of the 25-state body.
"Calls for violence, and for the destruction of any state, are manifestly inconsistent with any claim to be a mature and responsible member of the international community," the statement said.
Israeli Vice-Prime Minister Shimon Peres said the remark contravened the UN's charter and was "tantamount to a crime against humanity".
'World without Zionism'
Mr Ahmadinejad told some 3,000 students in Tehran that Israel's establishment had been a move by the West against the Islamic world.
He was addressing a conference entitled The World without Zionism and his comments were reported by the Iranian state news agency Irna.
"As the Imam said, Israel must be wiped off the map," he said, referring to Iran's late revolutionary leader, Ayatollah Ruhollah Khomeini.
In 2001, former Iranian president Hashemi Rafsanjani speculated that a Muslim state that developed a nuclear weapon might use it to destroy Israel.
His comments were part of a critique of what hew called American imperialism in the region.
Such calls are regular slogans at anti-Israeli or anti-US rallies in Iran.
Mr Ahmadinejad warned leaders of Muslim nations who recognised the state of Israel that they faced "the wrath of their own people".
Mr Ahmadinejad came to power earlier this year, replacing Mohammad Khatami who had sought better relations with the West.