Three gunmen opened fire Friday at one of President Mahmoud Ahmadinejad's campaign offices in the southeast, wounding three people, Iran's official news agency reported.
The shooting took place in Zahedan a day after a bombing at a Shiite mosque in the city killed 25 people.
The report by the Islamic Republic News Agency quoted the campaign office chief, Mohammad Zahed Sheikhi, as saying the three men threatened people before opening fire, injuring two office workers and an infant.
Sheikhi said the men were captured after a short chase.
Ahmadinejad and three other candidates are competing in the June 12 presidential election.
Deadly mosque blasts
Iran blamed the U.S. and Israel for the bombing Thursday at the mosque in Zahedan, saying the countries were trying to stoke sectarian tension with the Sunni Muslim minority.
"I announce that ... those who committed the bombing are neither Shiite nor Sunni. They are Americans and Israelis" who want to stoke sectarian conflict in the country, Iranian Interior Minister Sadeq Mahsouli said on the ministry's Web site.
Iran has repeatedly accused the U.S. and other Western countries of backing militants and opposition groups in the country, charges they have denied. The blame could be intended to mask real sectarian issues between Iran's Sunnis and majority Shiite population.
Zahedan has been the scene of attacks by an Islamic militant group called Jundallah that claims to be fighting for the rights of Sunnis and is believed to have al-Qaida links. The remote city, 1,000 miles southeast of Tehran near Pakistan and Afghanistan, also has been the scene of frequent clashes between drug smugglers and Iranian police.
The United States condemned the attack. Robert Gibbs, White House press secretary, said Friday: "The American people send their deepest condolences to the victims and their families. No cause justifies terrorism, and the United States condemns it in any form, in any country, against any people."
At the State Department, spokesman Ian Kelly noted that the target of the attacks served Muslims of Iran's Shiite majority sect and coupled it with recent violence against Shiite mosques elsewhere.
"We note with concern a recent trend of bombings of Shia mosques in Iraq and Pakistan, as well as in Iran, and strongly condemn any kind of sectarian-driven violence," Kelly said.
Asked about the Iranian accusation of U.S. complicity in the attack, Kelly said: "We do not sponsor any form of terrorism anywhere in the world. Never have, never will."
Jalal Sayyah, a senior security official in Zahedan, said 145 people were injured in the bombing Thursday and three suspects had been detained.
"Hire of the terrorists by the U.S. was verified based on investigation," Sayyah told The Associated Press.
Sayyah did not say whether the terrorists belonged to a specific group. In 2007, Jundallah, or God's Brigade, killed 11 members of Iran's elite Revolutionary Guards in Zahedan.
Iran blamed a similar bombing of a Shiite mosque in the country's southwest in April 2008 on three men it said had ties to the U.S. The bombing in the city of Shiraz, located some 550 miles south of Tehran, killed 14 people.
Last month, Iran hanged the men, who the court said were members of a little known monarchist group that wants to overthrow the country's ruling Islamic establishment.