BASRA, Iraq (AP) — An explosion rocked the center of Iraq's southern city of Basra on Monday, killing at least four people and wounding four others, according to Iraqi security forces.

The blast sent a column of black smoke into the sky. The governor of Basra, Asaad al-Idani, told reporters on the scene that a motorcycle had exploded.

It was not immediately clear whether a bomb had been rigged to the motorcycle or if it was a suicide bombing. The governor said two nearby cars were set ablaze from the explosion.

Iraq's Security Media Cell, an outlet affiliated with the country's security forces, said in a statement that four people were killed and four wounded as a result of the fire in two cars that were near the motorcycle.

It said forensics teams were at the scene of the blast and that more details would be released on the nature of the explosion, once investigations were completed.

Explosions have been rare in Basra in recent years, particularly since the defeat of the Sunni militant Islamic State group in 2017.

The oil-rich Basra is predominantly Shiite. No one immediately claimed responsibility for the explosion.

There has been an increase in political instability in Iraq following the Oct. 10 parliament elections which saw Shiite cleric Muqtada al-Sadr emerge as the biggest winner. Shiite armed factions loyal to Iran which lost around two thirds of their parliamentary seats have rejected the results of the election, alleging fraud.