The United States has granted visa to Iranian President Mahmoud Ahmadinejad to attend the United Nations summit in New York despite legal objections raised by the department of homeland security.

The state department granted visa to the newly-elected President, overruling concerns by the department of homeland security, which suspects that Ahmadinejad participated in the hostage taking at the US embassy in Iran in 1979.

"At the state department's request, the department of homeland security waived this ineligibility to allow the Iranian president, as Iranian head of government, to attend the general assembly and high-level summit," department spokesman Sean McCormack said on Wednesday.

McCormack said Ahmadinejad had at first been considered "ineligible" under the US Immigration Nationality Act because of the homeland security department's suspicions.

The law "applies when we have, 'reason to believe', that the visa applicant is within the scope of that broad provision covering a wide range of past and present activity that is supportive or in furtherance of terrorist activity," he said.

The Bush administration has been probing whether Ahmadinejad, elected in June, was involved in the 1979-81 seizure of the US Embassy in Tehran.

The student-led takeover resulted in the holding of 52 American diplomats as hostages for 444 days.

The issue arose when half a dozen former hostages said they recognised Ahmadinejad as one of the student leaders at that time, a claim denied by Tehran and disputed by several other former hostages.

Iran: Tough nut for US to crack