NEW YORK — Efforts led by the United States and Israel to isolate Iran suffered a setback Wednesday when the United Nations announced that Ban Ki-moon, the secretary-general, would join officials from 120 countries in Tehran next week for a summit that Iran has trumpeted as a vindication of its defiance and importance in world affairs.
Ban’s decision to go to the meeting of the Nonaligned Movement, announced by his spokesman, Martin Nesirky, came despite objections from both the Americans and Israelis, including a phone call from Prime Minister Benjamin Netanyahu of Israel. The decision was announced a few days after the president of Egypt, a nation long estranged from Iran, said he would attend the summit as well.
Ban’s decision to participate, which might have gone unnoticed in other years, was particularly fraught now because of the tensions with Tehran. Iran has defied UN Security Council resolutions to halt uranium enrichment and has backed the Syrian government’s repression of an armed uprising, a crackdown that Ban has condemned.
He has also castigated anti-Semitic statements and calls for Israel’s destruction made by Iranian leaders, reminding them that the UN Charter bans one member from threatening the existence of another.
But many diplomats and others said it would have been extraordinarily hard for Ban not to go. The 120 nations that are in the Nonaligned Movement represent the biggest single voting bloc in the 193-member General Assembly at the Unied Nations. It is customary for the secretary general to attend the movement’s annual meetings regardless of political sensitivities involving the host nation.
Taken together, the moves reinforced Iran’s contention that a reordering of powers is underway in the Middle East, where Western influence is waning, and US-Israeli efforts to vilify Iran as a rogue state are not resonating in much of the world.
Acknowledging that Ban has been under pressure not to attend, Nesirky said Ban viewed the visit as an opportunity to raise all of these issues directly with his Iranian hosts.
''The secretary general is fully aware of the sensitivities of this visit,’’ Nesirky told UN reporters. ‘‘He’s heard the views of some of those who said he should not go. At the same time, the secretary general has responsibilities that he is determined to carry out.’’
Nesirky also said Ban expected to meet with senior Iranian leaders, including Ayatollah Ali Khamenei. ‘‘It is certainly the secretary general’s expectation that he will have meaningful and fruitful discussions with the supreme leader,’’ he said. To boycott the invitation from Iran, he said, ‘‘would be a missed opportunity.’’
The summit of the Nonaligned Movement, a group formed during the Cold War, includes a number of other countries that the United States has sought to marginalize, among them North Korea and Sudan, whose president, Omar Hassan al-Bashir, is wanted under a war crimes indictment by the International Criminal Court.
There was no immediate reaction to Ban’s decision from Israel. But according to Netanyahu’s office, he phoned Ban on Aug. 10, telling him that such a trip, even if well-intentioned, would be a mistake.
The reaction to Ban’s announcement was more muted in the Obama administration. Some administration officials tried to put the best face on the situation, urging Ban to exploit the moment to convey his unhappiness with Iran’s actions.
‘‘We think that Iran is going to try to use the event for propaganda purposes,’’ said Tommy Vietor, speaking for the National Security Council.