Iraqi security forces have clashed with fighters from the Mahdi Army of Shia leader Muqtada al-Sadr in the southern city of Basra, amid demands by the group that detained members be released.

Mortar and gun fire was heard on Tuesday after security forces entered the neighbourhood of al-Tamiya, a Mahdi Army stronghold, the AFP news agency said.

Clashes later spread to five other neighbourhoods, including al-Jumhuriya, Five Miles and al-Hayania, the Mahdi Army's main stronghold in Basra, 550km south of Baghdad.

"We began operations at 5am [0200 GMT]," Major Karim al-Zubaidi, a police spokesman, said.

"There is fighting between security forces and the Mahdi Army."

The fighting erupted soon after a night-time curfew was imposed on Basra province, and hours after Nuri al-Maliki, the prime minister, arrived in the city for a visit.

Basra province was handed over to Iraqi control by British  forces in mid-December.

Security operation

General Mohan al-Furayji, the Iraqi commander in charge of security in the south of Iraq, announced late on Monday the launch of a security operation throughout Basra province.

Vehicle access would be temporarily closed from neighbouring provinces during the evening hours from Wednesday and until Friday, he said.

Teaching at schools and universities has been suspended from Tuesday until Thursday.

Al-Furayji said the security sweep was designed to "impose the law and chase the criminals."

But Harith al-Athari, a spokesman for al-Sadr's bloc in Basra, accused the government of trying to purge the Mahdi Army of members who refused to heed orders by al-Sadr for a ceasefire.

'Situation bad'

"The situation is bad and we regret the fighting. We are ready for negotiations and want to calm things," al-Athari said.

Al-Sadr has instructed the Mahdi Army to maintain its unilateral ceasefire across Iraq in recent weeks.

However, the US military and Iraqi security forces have detained al-Sadr loyalists they accuse of belonging to breakaway armed factions.

Al-Sadr's followers say al-Maliki's government has targeted his supporters in the run-up to provincial elections later this year.

Call for strike

Amid the security operation in Basra, leaders of al-Sadr's bloc in Baghdad called for its supporters to close their shops and businesses in protest at members' arrests.

The call was heeded on Monday in Amil and Baiyaa, two predominantly Shia neighbourhoods of Baghdad.

Police said Mahdi Army members issued general strike orders in three other areas of southwestern Baghdad and in Mahmudiya, about 30km south of the capital.

"This civil disobedience may be called for in the rest of Baghdad and maybe in southern provinces if the government does not free our detainees," Ali al-Mayali, a politician loyal to al-Sadr, said on Monday.

Liwa Smeism, a senior political adviser at al-Sadr's office in Najaf, said the strikes in west Baghdad would continue for up to 48 hours unless the government released detainees loyal to the movement.

PHOTO CAPTION

An Iraqi soldier mans a checkpoint in the southern city of Basra.

Al-Jazeera