A successful conclusion of current talks over the disputed program would strengthen the Islamic Republic and its allies in the region, said Sheik Hassan Nasrallah, whose group is backed by Iran and Syria.
Talks between Iran and six world powers - the U.S., France, Russia, China, the United Kingdom and Germany - ended over the weekend without an agreement on a preliminary deal that would have set the stage for broader talks. Diplomats said talks broke down in part because the international powers refused to formally recognize Iran's right to enrich uranium.
Iran insists it is not pursuing a bomb and only wants to enrich uranium for energy and medical applications.
Negotiations are due to resume in Geneva on November 20. In exchange for nuclear concessions from Iran, the U.S. and world powers are offering Tehran limited and reversible relief from economic sanctions that have strained its economy.
"Regarding Iran's nuclear program, they will either reach an agreement or disagree and the situation heads to war," Nasrallah told hundreds of supporters in a rare public appearance in a giant hall south of Beirut to attend a Shi'ite Muslim religious ceremony.
"If war breaks out, everyone should be worried but others should be worried more than us," Nasrallah said.
"If an understanding is reached between Iran and the West over the nuclear program, our side will be stronger locally, regionally and internationally," Nasrallah said. He also warned Arab countries against betting on the fall of Syrian President Bashar Assad's government, saying that they will be proven wrong.
Nasrallah stood in front of hundreds of supporters who pushed forward to see him while chanting "at your service Nasrallah."
Nasrallah has made few public appearances since his group fought a 34-day war with Israel in 2006 for fear of assassination by Israeli forces.
In his first public appearance since August 2, the black-turbaned Shi'ite cleric also said that his arch-enemy Israel is happy to see Sunni and Shi'ite Muslims killing each other.
Nasrallah usually gives his speeches from secret locations and speaks through a television link.
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