Four bombs exploded Sunday in the capital of the only province of Iran dominated by ethnic Arabs, followed hours later by a fifth bomb in the center of Tehran.
State media reported that at least nine people were killed in the attacks, which came five days before Iranians are scheduled to elect a new president. The violence was called the most serious in this country in more than a decade.
The wave of bombings in Ahvaz, in Khuzestan province near the border with Iraq, came over a two-hour period Sunday morning. One device exploded outside the governor's office, possibly after being placed in a car, state television reported. Another detonated outside the state housing office. The third and fourth were placed near the home of the head of state television and radio in the province.
At least 30 people were wounded, according to state television.
The explosion in Tehran, the national capital, came hours later and killed two people, according to the official Islamic Republic News Agency. Witnesses said the blast was set off in a garbage can near a fruit-and-vegetable market.
"These bombings are aimed at discouraging people from participating in the election, but these terrorist acts would have the reverse effect," former president Ali Akbar Hashemi Rafsanjani, a candidate in the elections, said in an interview on state television.
Nasser Shabani, deputy commander of Tehran's police force, said a suspect in the Tehran bombing was arrested but offered no details, local news media reported. He put the number of wounded at 12.
The four bombings in Iran's southwest drew fresh attention to Khuzestan province. Two months ago, hundreds of people rioted in Ahvaz and several were reported killed.
The hardscrabble province is home to most of the 2 million Arabs who reside in Iran, many of whom complain about employment discrimination at the hands of the ethnic Persians who have traditionally ruled the country of 70 million.
Other ethnic minorities in Iran make similar complaints, but dissatisfaction in Khuzestan is made vivid by the presence of several profitable oil fields, where few ethnic Arabs are able to find work.
The relative poverty of the province is further highlighted by the wreckage that remains in the countryside, where much of the worst fighting of Iran's 1980-88 war with Iraq took place.
The April riots followed the circulation of an evidently forged official letter urging that non-Arabs be relocated to Ahvaz to dilute the Arab majority there. The controversy focused attention on underground groups that promote pan-Arab calls for the area to be annexed by Iraq.
Security forces working for Iran's theocratic government arrested hundreds of people after the unrest, and closed off the province to foreign reporters. Al-Jazeera, the Arabic-language satellite news channel, was ejected from the country after officials accused it of encouraging unrest through its reporting.
The bombings came as scores of international journalists were in the country to cover the presidential election set for Friday.
Eight candidates are vying to replace President Mohammad Khatami, the reformist ending his second and final term. Public opinion surveys show Rafsanjani, often described as a pragmatist, leading the field, which includes four hard-line conservatives. The leading reformist candidate, Mostafa Moin, a former higher education minister, has campaigned extensively in the provinces and last week was the first candidate to visit Khuzestan.
In an unrelated development, several hundred women staged a sit-in outside the front gate of Tehran University. The protesters raised chants and demanded rights revoked after the 1979 Islamic revolution. They taunted the police and plainclothes security officers who formed a perimeter around the demonstrators, pushing away women and men who attempted to join the group.
The authorities also cut off cellular phone service in the area. As they challenged reporters near the site, they briefly confiscated the video camera of actor Sean Penn, who is in Iran accredited as a reporter for the San Francisco Chronicle.
Special correspondent Mehrdad Mirdamadi contributed to this report.