BAGHDAD (AP) — The Iraqi government says security forces have launched a search operation to determine the source of three mortar shells that landed inside Baghdad's heavily fortified Green Zone, the first such attack in several years.

The shells landed just after midnight on Friday in an abandoned lot and there were no casualties, it says.

There was no immediate claim of responsibility for the attack, which comes amid worsening protests against poor services and unemployment in the southern city of Basra, which have turned violent in the past few days.

Hundreds of protesters on Thursday night set fire to a government building as well as the offices of Shiite militias. At least three people were shot dead in confrontations with security forces.