The US has risked inflaming tensions with Iran by blocking the entry of Tehran’s chosen envoy to the United Nations.
Tehran had named Hamid Aboutalebi as its envoy but his selection was seen as provocative since he was said to a member of the group that stormed the US embassy in Tehran in 1979 and held 52 Americans hostage for more than a year.
Attempts by the US to persuade Iran to nominate someone else failed and the white House has now announced it will not issue Aboutalebi with a visa to enter the US, where the UN is based.
White House spokesman Jay Carney said: "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. Our position is that we will not be issuing him a visa."
Officials said Undersecretary of State Wendy Sherman, the chief U.S. negotiator in the nuclear talks, informed Iranian officials involved in discussions in Vienna this week about the visa decision. The White House said it did not expect the negotiations, which are due to resume next month, to be affected.
However, Hamid Babaei, a spokesman for the Iranian UN Mission, accused the US of being in breach of international law and in contravention of “the obligation of the host country and the inherent right of sovereign member-states to designate their representatives to the United Nations".
Aboutalebi maintains his involvement in the group, Muslim Students Following the Imam's Line, that took over the embassy was limited to translation and negotiation.
The US is normally obliged to allow UN delegates to enter the country but an exception can be made if a visa applicant is found to have spied against the US or be a threat to its national security.