A bomb blast in northwestern Iran killed at least 11 people and injured dozens on Wednesday, local media reported.

The explosion happened during a military parade in the northwestern town of Mahabad in West Azarbaijan province.

Iran's Press TV reported that 11 people were killed in the explosion.

Also, the local semi-official Fars news agency quoted a medical source in Mahabad's Imam Khomeini hospital that "11 individuals were martyred in the bombing carried out by anti-Revolution elements."

"The number of the injured people has reached 58. Two of the wounded are in critical conditions and have been transferred to Orumiyeh (provincial capital city of West Azarbaijan)," Fars reported.

Meanwhile, Qolamreza Masoumi, chief of the country's emergency center, said that the explosion during the military parade has killed 12 people, according to the semi-official ISNA news agency.

The number of the injured has risen to 81, an unnamed medical official in the Mahabad hospital was quoted by ISNA as saying.

The explosives had been placed in a holdall and went off when people were watching the parade, the report said.

Vahid Jalalzadeh, governor of West Azarbaijan province, told the official IRNA news agency that the killed were mostly women and children, adding "anti-Revolution agents have always carried out such brutal acts to take revenge on the people of Mahabad who are always in the scene."

Ali Nikbakht, director general of political affairs of the West Azarbaijan, said the incident is under investigation.

No group or individual has claimed responsibility for the explosion.

Iran's West Azarbaijan province witnessed regular armed clashes between Iranian security forces and Kurdish militant parties, in particular Party of Free Life of Kurdistan (PJAK), an anti-Iran Kurdish group linked to Turkey's outlawed Kurdish Workers' Party ( PKK).

The Iranian armed forces staged military parades all throughout the country on Wednesday to mark the start of the Week of Defense, commemorating Iranian sacrifices during the eight-year Iraq-Iran war in the 1980s.

In the parades, Iran's most advanced military power and abilities are usually showcased.