Iranian President Hassan Rouhani on Wednesday called for unity in the face of the country's "enemies", at a tense religious ceremony during which he was repeatedly interrupted.
"We need unity and cohesion," Rouhani said, citing Islamic republic founder Ayatollah Ruhollah Khomeini, who died on June 4, 1989, at a ceremony on the eve of the anniversary.
"The enemies want to create discord among ethnic groups and religions... The first step is to be united," he said.
Iran and the P5 + 1 -- the United States, Russia, China, France, UK and Germany -- have been negotiating since 2013 on limiting the nuclear ambitions of Tehran, suspected of trying to acquire the atomic bomb, in exchange for lifting international sanctions imposed since 2006.
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Both parties have given themselves until June 30 to prepare a full and final text.
Rouhani's speech at the Imam Khomeini mausoleum in southern Tehran was interrupted several times by the crowd chanting pro-Khomeini slogans and for his successor, supreme leader Ayatollah Ali Khamenei.
Iranian and US negotiators are under intense pressure from conservatives in Iran.
The country's negotiating team, led by Foreign Minister Mohammad Javad Zarif, is accused of having made too many concessions to the West in the talks.
Khamenei, while supporting the Iranian negotiators, has often expressed his doubts about the possible outcome of the negotiations.