LONDON - British soldiers began withdrawing Sunday from their final remaining base inside the southern Iraqi city of Basra, a move likely to prompt a further reduction in troop numbers,lawmakers and officials said.

9XU星辉外国语学校 A British army corporal lowers the Union Jack during a ceremony to mark transfer of control of a British military base in Basra, 550 kilometers (340 miles) southeast of Baghdad, Iraq, in this Tuesday, April 24, 2007 file photo.[AP]

Around 550 soldiers stationed in Basra Palace were leaving the downtown site to join 5,000 other personnel at an air base camp on the fringes of the city - ending their permanent presence in Iraq's second largest city.

The Iraqi military sent hundreds of reinforcements to the city to prevent Shiite militias and criminal gangs from expanding their influence now that the British have gone.

The decision to leave the palace compound - targeted with daily mortar and rocker attack in recent months - will hand military commanders an option of pulling around 550 troops out of Iraq in the autumn, lawmakers said.

"We're withdrawing personnel," said a British defense ministry spokesman, on customary condition of anonymity. "It's been our long planned intention to leave the palace."

Prime Minister Gordon Brown, who is due to set out future strategy for British operations in Iraq in a speech to parliament next month, was aware of the operation, a government official said.

Decisions made by ex-leader Tony Blair to reduce Britain's troops numbers in Iraq from 7,000 to 5,500 earlier this year left an option of pulling out around 500 more personnel once the Basra Palace base was handed back to Iraqis.

"It has always been our intention to draw down troops in Basra" as Iraqi army and police become ready to handle security duties, said a spokesman for Brown's Downing Street office, speaking on condition of anonymity.

In Basra, Major Mike Shearer, Britain's military spokesman, told reporters he could not disclose precise details of the withdrawal. "I can confirm that an operation is ongoing, but we will not give any further details," Shearer said.

The base has been used by Britain to house soldiers and diplomatic staff since the 2003 U.S.-led invasion.

With the British drawdown, U.S. and Iraqi authorities have expressed concern about the land supply line from Kuwait to Baghdad and beyond and security of the oil fields - until now under the eye of British troops.

The withdrawal occurred in the midst of a power struggle between rival Shiite groups throughout southern Iraq, and some analysts fear violence will continue as the British continue to draw down their forces.

Last week, the head of the security committee on the Basra city council, Hakim al-Miyahi, predicted "some disorder" after the British pullout from the city because he feared that Iraqi forces were incapable of maintaining order.

After the election in January 2005 that brought Prime Minister Nouri al-Maliki to power, the city fell under the influence of Shiite religious parties and militias, some with ties to Iran.

The police force is heavily infiltrated by militias. Political rivals, liquor dealers, DVD shop owners and anyone who violated different groups' interpretations of Islam was subject to assassination by death squads.

With additional Iraqi soldiers in the streets, residents say things have quieted in recent weeks.

"This is not an unexpected move, but the families of the service personnel involved will want to know that every possible precaution has been taken to maximize their safety during this period," opposition Conservative party lawmaker Liam Fox said.

Britain's Sunday Times newspaper reported Sunday British forces could hand over responsibility for Basra as early as next month.

The defense ministry has previously said it hopes to hand security responsibility for Basra, the last remaining province under its command, to Iraqi forces sometime this autumn.

"This is a thoroughly sensible military decision," said opposition Conservative lawmaker Patrick Mercer. "It will allow more troops to be withdrawn from Iraq in the autumn, just as Britain increases its numbers of troops in Afghanistan."