Four bombs exploded in Ahvaz, the capital of Khuzestan province, killing nine people and wounding dozens of others. The bombings all happened within a two-hour period, apparently targeting provincial government buildings and homes of government officials.
A fifth bomb went off near a vegetable market in Tehran, the national capital, killing one person.
Iranian security officials said they made one arrest in connection with the bombings. Bombings have been rare in Iran since the end of its war with Iraq in 1988.
"These bombings are aimed at discouraging people from participating in the election, but these terrorist acts would have the reverse effect," said former president Ali Akbar Hashemi Rafsanjani, a leading candidate in Friday's presidential election, according to the Washington Post.
Khuzestan province, where four of the bombings took place, shares a border with Iraq and is dominated politically by ethnic Arabs. Violent protests broke out there in April when Arabs marched in opposition to an alleged plan to dilute Arab political power by settling more Persians in the area.
Overall Arabs make up 3 percent of Iran's population, while Persians account for 51 percent. Media reports from the area said it was unclear whether the bombings were related to the April protests.
Ali Agha Mohammadi, a spokesman for the Supreme National Security Council said the bombings in the province were the work of groups affiliated with Saddam Hussein's former Baathist regime in Iraq, the Associated Press reported.