LONDON, April 12 — The US has refused to issue a visa to Iran’s UN envoy-designate for being involved in the siege of the US embassy in Tehran in 1979, a media report said Saturday.

This decision has prevented Hamid Aboutalebi from taking up his position at the UN headquarters in New York, BBC reported.

White House spokesman Jay Carney said Friday that the UN and Iran had been told “that US will not issue a visa to Aboutalebi”.

The US House of Representatives and the Senate have both voted in favour of a bill barring Aboutalebi from entering the US, the report said.

The bill still requires US President Barack Obama’s signature for it to become a law.

However, Iran has said that Aboutalebi is one of its most experienced diplomats and stands by his nomination.

Aboutalebi has denied being a part of the group that took over the US embassy in Tehran in 1979.

Fifty-two US diplomats and citizens were held hostage for 444 days (November 4, 1979, to January 20, 1981) by pro-Iranian Revolution students.

The hostage crisis came as a blow to the US, which had supported the overthrow of the then Iranian ruler, Mohammad Reza Pahlavi.

In an interview with an Iranian news site last month, Mr Aboutalebi said he was not part of the group that took over the US embassy and was only later asked to translate for the students.

The 52 Americans were held for 444 days during the crisis.

It is believed the US has never before denied a visa for a UN ambassador and correspondents say there is concern among diplomats about the precedent that could be set.–Agencies