Mortar shells pounded Iraqi capital Baghdad's fortified green zone Wednesday, killing a civilian and injuring four, while the Iraqi government gave Shia fighters in Basra 72 hours to lay down arms, according to media reports.

'Three mortar shells fell Wednesday morning on the green zone,' a witness in the zone told the Voices of Iraq (VOI) news agency.

Another witness told the agency that a second mortar shell landed on a building opposite the ministry of foreign affairs in the protected area, killing a civilian and injuring four.

The green zone is home to the US embassy and other diplomatic missions and Iraq's cabinet, parliament and many ministries.

The area has come this week under barrages of rockets and mortar shells.

Iraqi officials could not ascertain whether a surge in attacks on the area was related to unrest in Basra and other cities in southern Iraq, involving Shia militiamen.

In another development, the Iraqi government gave Shia fighters in Basra 72 hours to hand in their arms, the Dubai-based al-Arabyia television reported.

Heavy fighting between Iraqi security forces and Shia fighters in Basra raged Wednesday for the second day, leaving at least 30 people dead.

Fighting broke out in Shia-dominated al-Sadr City in eastern Baghdad, in which at least 10 people were killed, according to al-Arabyia.

The intensity of the fighting between Iraqi troops and Mahdi fighters kept many people home. Schools and shops closed as security checkpoints were set up in and around the poor neighbourhood, which is the stronghold of the Mahdi Army, which is loyal to radical cleric Moqtada al-Sadr.