Reports from Iran say a bomb has exploded in the southeast of the country, the second bombing in the area in the past week.
Iranian news agencies say the bomb blew up late Friday in the city of Zahedan. It is not clear if there were any casualties.
The semiofficial Fars news agency says there was shooting between Iranian police and armed men after the explosion.
On Wednesday, a car bomb blast in the same city killed 11 members of Iran's Revolutionary Guards Corps.
A Sunni Muslim militant group, Jundollah (God's Brigade), claimed responsibility for that attack. Officials say the group is linked to al-Qaida.
Iran is largely Shi'ite but has a Sunni minority.
Zahedan is the capital of Sistan-Baluchistan province, which borders Pakistan and Afghanistan.
Iran has accused the United States of backing militants in the sensitive border area to destabilize the country.