The United States will not grant a visa to Tehran's newly appointed UN ambassador, Hamid Aboutalebi, who has been linked to the 1979 US hostage crisis, the White House says.
"We have informed the United Nations and Iran that we will not issue a visa for Mr Aboutalebi," White House spokesman Jay Carney said.
As the host government, the United States generally is obliged to issue visas to diplomats who serve at the United Nations, although there have been exceptions.
Carney said the White House was studying constitutional and other concerns surrounding a bill, which overwhelmingly passed Congress and bars Aboutalebi from US soil and did not say whether President Barack Obama would sign it.
"We certainly share the intent of the bill passed by Congress," Carney said.
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Carney also said that there was no reason to expect that the row between Tehran and Washington over the envoy would impact progress in talks between Iran and world powers, including the United States, over Tehran's nuclear program.
Iran had slammed as unacceptable a previous US statement that the nomination of Aboutalebi was "not viable".
Aboutalebi, a veteran diplomat who currently heads President Hassan Rouhani's political affairs bureau, has insisted he was not part of the hostage-taking in November 1979, when a Muslim student group seized the US embassy after the overthrow of the pro-Western shah.
He has acknowledged he served a limited role as a translator for the students, who took 52 Americans hostage for 444 days.
But the bill passed by both chambers of Congress and sent to Obama's desk on Thursday brands Aboutalebi as a "terrorist" and politicians say he should not be allowed to walk around the streets of New York with diplomatic immunity.
