WASHINGTON — In a rare diplomatic rebuke, the United States has blocked Iran’s controversial pick for envoy to the United Nations, a move that could stir fresh animosity at a time when Washington and Tehran have been seeking a thaw in relations.The Obama administration said Friday that the U.S. had informed Iran it would not grant a visa to Hamid Aboutalebi, a member of the group responsible for the 1979 takeover of the U.S. Embassy in Tehran. While U.S. officials had been trying to persuade Iran to simply withdraw Aboutalebi’s name, the announcement amounted to an acknowledgment that those efforts had not been successful.“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 embassy takeover. He has insisted his involvement in the group Muslim Students Following the Imam’s Line was limited to translation and negotiation.Hamid Babaei, a spokesman for the Iranian U.N. Mission, said the decision was not only regrettable but “in contravention of international law, the obligation of the host country and the inherent right of sovereign member-states to designate their representatives to the United Nations.”As host country for the United Nations, the U.S. must provide rights to persons invited to the New York headquarters. However, exceptions can be made when a visa applicant is found to have engaged in spying against the U.S. or poses a threat to American national security.Denying visas to U.N. ambassadorial nominees or to foreign heads of state who want to attend United Nations events in the U.S. is extremely rare, though there appears to be precedent. According to a paper published by the Yale Law School, the United States rejected several Iranians appointed to the U.N. in the 1980s who had played roles in the embassy hostage crisis or other acts against American citizens.Iran’s choice of Aboutalebi had pinned President Barack Obama between congressional pressure to deny the envoy entry into the U.S. and the White House’s delicate diplomatic dealings with Tehran. After more than three decades of discord, U.S. and Iranian officials have started having occasional direct contact, including a phone call last fall between Obama and new Iranian President Hassan Rouhani. The U.S. and its international partners also have reached an interim agreement with Iran to halt progress on Tehran’s disputed nuclear program. Officials are in the midst of negotiating a long-term agreement to prevent Iran from building a nuclear weapon.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 by the matter.Despite some signs of progress in relations, many U.S. lawmakers continue to eye Iran skeptically, and Tehran’s choice of Aboutalebi sparked outrage from both Democrats and Republicans. The House and Senate unanimously passed legislation expanding the grounds for barring entry into the U.S. to include individuals engaged in terrorism.Carney would not say Friday whether Obama would sign that bill, but he said the president did share its sentiments.The administration’s decision to block Aboutalebi’s nomination drew praise from both parties, including Sen. Ted Cruz, R-Texas, the chief sponsor of the congressional legislation. In an interview with Fox News, Cruz said he appreciated the president “doing the right thing and barring this acknowledged terrorist from coming into the country.”Sen. Chuck Schumer, D-N.Y. said allowing Aboutalebi into the U.S. “would have been a slap at all American victims of terrorism, not just those taken hostage in 1979. We’re glad the Obama Administration made this choice, and Iran should stop playing these games. “U.N. officials had no immediate comment on the U.S. decision.Iran had previously called U.S. rejection of Aboutalebi “not acceptable,” with Iranian state television quoting Foreign Ministry spokeswoman Marzieh Afkham as saying he is one of the country’s best diplomats and arguing that he previously received a U.S. visa.American officials said Iran still has time to withdraw the nomination and application, suggesting the U.S. has simply chosen to not act on the visa instead of outright rejecting it.Without a U.S. visa, Aboutalebi would not be allowed to enter the United States. Iran could nominate a different ambassador or have Aboutalebi occupy the post from overseas.Despite the decades-long tensions between the U.S. and Iran, the Islamic republic maintains a robust diplomatic mission at U.N. headquarters in New York. The U.S. frequently allows visas for representatives from countries it disfavors, including Syria and North Korea, but restricts their diplomats’ movements and activities to a 25-mile radius of New York City.There have been previous instances where officials accused of terrorism or deemed to pose a threat to the U.S. have sought visas to appear at the U.N., including with a previous Iranian nominee in the early 1990s and more recently with Sudanese President Omar el-Bashir. In most cases, the U.S. has either signaled opposition to the applicant and the request has been withdrawn, or the State Department has simply declined to process the application.