The United Nations said on Tuesday that Secretary-General Ban Ki-moon has congratulated Iranian President Mahmoud Ahmadinejad,
whose contested re-election sparked violent protests across the country.
"The letter went out yesterday," said UN spokeswoman Marie Okabe.
June 12 election, which secured hardline President Ahmadinejad's re-election, plunged Iran into its biggest internal crisis since the 1979 Islamic revolution, exposed deepening divisions in its ruling elite and set off a wave of protests that left 26 people dead.
Western leaders, already upset by Ahmadinejad's anti-Israel rhetoric, Holocaust denial and uncompromising nuclear line, refused to congratulate the president on his inauguration last week, although their counterparts in Japan and Turkey did so.
Among those leaders who withheld their congratulations to Ahmadinejad were US President Barack Obama, British Prime Minister Gordon Brown, French President Nicolas Sarkozy and German Chancellor Angela Merkel.
The UN spokeswoman said Ban's letter was a "customary letter on occasion of inauguration" but added that the text would not be made public. The secretary-general routinely congratulates leaders after elections and the UN has released the content of some of those messages in the past.
Separately, Nobel Peace Prize laureate Shirin Ebadi on Tuesday urged Ban to visit Iran to receive a first-hand account of human rights abuses.
"I ask UN Secretary-General Ban Ki-moon to visit Iran," Ebadi told reporters in Seoul, where she picked up a local peace prize. "He must speak to the families whose members have been arrested or killed."
Ban is also in South Korea, though it was not immediately clear whether he and Ebadi had spoken.
The secretary-general's press office had no immediate reaction to Ebadi's remarks. Last month Ban told a news conference that he was closely monitoring the situation in Iran but that he had made no decision on whether he should send an envoy to investigate reports of human rights abuses there.
Ebadi says that more than 100 people have been killed.
Amnesty International, Human Rights Watch and other rights groups have urged Ban to send a representative to Iran and press for the release of those arrested after the election.
Ahmadinejad is expected to come to New York next month to attend the annual UN General Assembly gathering of world leaders.
The UN Security Council has imposed three rounds of sanctions on Iran over its nuclear program.