The number of people killed in a shooting attack on a military parade in southwestern Iran on Saturday has risen to 24, the official state news agency IRNA said.

"There are a number of non-military victims, including women and children who had come to watch the parade," the agency quoted an unnamed official source as saying.

A video distributed to Iranian media showed soldiers crawling on the ground as gunfire blazed in their direction. One soldier picked up a gun and got to his feet as women and children fled for their lives.

State television said the assault, which wounded more than 60 people, targeted a stand where Iranian officials had gathered to watch an annual event marking the start of the Islamic Republic's 1980-88 war with Iraq.

A senior Iranian Revolutionary Guards official vowed retaliation for the gun attack that killed at least 24 people at a military parade on Saturday, the official news agency IRNA reported.

"Enemies should not imagine that they can gain dignity with this sinister move. The Iranian people and the armed forces will respond to this," Yahya Rahim Safavi, a senior Revolutionary Guards official, was quoted by IRNA as saying.

"Shooting began by several gunmen from behind the stand during the parade. There are several killed and injured," a correspondent told state television.

Four militants carried out the attack and two of them were killed, according to ISNA.

The semi-official news agency Mehr said further shooting broke out as some of the attackers who managed to escape were being chased.

An anti-government Arab group, the Ahvaz National Resistance, is responsible for Saturday's attack on a military parade in Iran's southwestern city of Ahvaz, a spokesperson told Reuters.

Yaghub Hur Totsari, spokesman for one of the two groups that identify themselves as the Arab Struggle Movement for the Liberation of Ahvaz, said the Ahvaz National Resistance, an umbrella organization of all armed movements, was behind the attack but did not specify which group.

Totsari identified one of the assailants by the initials A.M., without elaborating.

The Islamic Revolutionary Guards Corp (IRGC) have been the sword and shield of Shia clerical rule since Iran's 1979 Islamic Revolution. The Guards also play a major role in Iran's regional interests in countries such as Iraq, Syria and Yemen.

Iran was holding similar parades in several cities including the capital Tehran and the port of Bandar Abbas on the Gulf.

Attacks on the military are rare in Iran.

Last year, in the first deadly attack claimed by Islamic State group in Tehran, 18 people were killed at the parliament and mausoleum of Ayatollah Ruhollah Khomeini, the founder and first leader of the Islamic Republic.