WASHINGTON: The United States, in a rare diplomatic rebuke, will not grant a visa to Tehran's pick for envoy to the United Nations, the Obama administration said on Friday.

The move could complicate efforts to thaw the decades-long diplomatic freeze between the US and Iran, as the two countries negotiate a deal to curb Tehran's disputed nuclear programme.

President Barack Obama's administration had previously said only that it opposed the nomination of Hamid Aboutalebi, who was a member of the group responsible for the 1979 takeover of the US Embassy in Tehran as a revolution erupted in Iran.

US officials had hoped the issue could be resolved by Tehran simply withdrawing the nomination.

That did not happen, so the US made the unusual, if not unprecedented, move to not grant a visa to a UN ambassadorial nominee.

''We've communicated with the Iranians at a number of levels and made clear our position on this – and that includes our position that the selection was not viable,” White House spokesman Jay Carney said.

“Our position is that we will not be issuing him a visa.''

Aboutalebi is alleged to have participated in a Muslim student group that held 52 Americans hostage for 444 days during the takeover. His nomination has outraged members of Congress, who passed a bill barring entry to the US to an individual found to be engaged in espionage, terrorism or a threat to national security.

Carney would not say whether Obama would sign the bill but said the president shares its sentiments.

United Nations officials had no immediate comment on the US decision.

Iran has called US rejection of Aboutalebi “not acceptable,” with Iranian state television quoting Foreign Ministry spokeswoman Marzieh Afkham as saying Aboutalebi is one of the country's best diplomats and arguing that he previously received a US visa.

Aboutalebi has insisted his involvement in the group involved in the embassy takeover, Muslim Students Following the Imam's Line, was limited to translation and negotiation.

Iranian officials said they had submitted a visa application for Aboutalebi, but it was unclear whether the US actually denied the request or simply decided not to act on it.

State Department spokeswoman Jennifer Psaki said the administration was prohibited from discussing the matter in detail because visa cases are confidential.

In past problematic visa cases for ambassadors and even heads of state – such as with a previous Iranian nominee in the early 1990s and more recently with Sudanese President Omar el-Bashir – the US has either signalled opposition to the applicant and the request has been withdrawn, or the State Department has simply declined to process the application.

Those options, as well as approving or denying the application, are available in the current case.

US immigration law allows broad rejection of visas to foreigners and, in many cases, authorities do not have to give an explicit reason why other than to deem the applicant a threat to national security or American policy.