Foreign Minister Ali Akbar Salehi said in New York that Iran could not support any country -- including ally Syria -- that used such weapons, calling this "a situation that will end everything."

"If any country... uses weapons of mass destruction, that is the end of the validity, eligibility, legality, whatever you name it, of that government," he said at a talk given to the Council on Foreign Relations think tank.

He was responding to a hypothetical question from the audience about Iran's reaction if fallout from chemical weapons drifted across the border in the event of the Syrian government there unleashing its chemical arsenal.

"Weapons of mass destruction, as we said it, is against humanity, something that is not acceptable," he said.

Iran suffered from Iraqi use of chemical weapons during the countries' 1980-1988 war and says it opposes all such weapons, although Western powers and Israel accuse Iran of trying to build a nuclear bomb.

The Syrian military has not used chemical weapons against the increasingly widespread rebellion. US Defense Secretary Leon Panetta has said the Syrian regime recently its chemical arms to help keep them safe.

"We have assured US officials that the Iraqi government is determined to land (Iranian) flights and carry out random searches," Zebari said, quoted by Arabic daily Al-Hayat.

The Iraqi minister added that his government had told Tehran "to stop the flights and stop arming or financing the (Syrian regime) or any other party to the conflict."

Zebari said Iraq would not "not accept being a transit point or passage way for... arming or financing" the Syrian conflict.

Last week, US Secretary of State Hillary Clinton pushed Baghdad to deliver on pledges to stop such flights during a meeting with Iraqi Vice President Kudayr al-Khuzaie.

Clinton reported "some encouraging first steps," citing an incident in which Iraqi authorities stopped a North Korean flight from crossing its air space while on its way to Syria over suspicions it was carrying arms and advisers.

Zebari said the flights first started in March and were stopped after the Iraqis called on the Iranians to do so. By late July, however, the flights resumed.

"They (the Iranians) said they were not carrying weapons or ammunition but pilgrims, visitors and other things," said Zebari, adding that "just to be sure, we will land these planes."

Washington has been calling on Baghdad to ensure that all Iranian planes flying over its air space are ordered to land and checked for weapons.

Tehran has told Iraqi Prime Minister Nuri al-Maliki the planes are carrying humanitarian aid to Syria, where the opposition has been fighting since last year to oust President Bashar al-Assad.

But many in the US government suspect the planes are ferrying military equipment to the Assad regime.