Tehran, April 12 (IANS): Iran's ambassador-designate to the UN cannot be replaced, an Iranian minister said Saturday.

The US has refused to issue a visa to Hamid Aboutalebi for being involved in the siege of the US embassy in Tehran in 1979.

"Iran will follow up Aboutalebi's case through legal channels," IRNA news agency quoted Iran's Deputy Foreign Minister for Legal and International Affairs Abbas Araqchi as telling.

The refusal of the visa has prevented Aboutalebi from taking up his position at the UN headquarters in New York.

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

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

Iran has rejected the decision as unacceptable and saying that it is against international laws.

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.