BAGHDAD - Armed looters ransacked an abandoned British base in southern Iraq on Friday as Iraqi soldiers guarding the camp stood by and watched, raising concerns that Iraqi troops are ill-equipped to take control of security from U.S.-led coalition forces.

A crowd of about 5,000, including hundreds armed with AK-47 assault rifles, attacked Camp Abu Naji and hauled away window and door frames, corrugated roofing and metal pipes, despite a 450-member Iraqi army brigade meant to guard the base.

"The looters stole everything, even the bricks," said Ahmed Mohammed Abdul Latief, 20, a student at Maysan University. "They almost leveled the whole base to the ground."

The last of 12,000 British troops left the camp in Amarah, the capital of southern Maysan province, on Thursday after continued mortar attacks by a local Shiite militia that residents said was controlled by anti-American cleric Muqtada al-Sadr.

Maj. Charlie Burbridge, a British military spokesman, said the Iraqi army maintained full control of the camp, even during the looting, and had managed to eject the thieves by evening. "Our confidence in the Iraqi security forces to maintain day-to-day order in Amarah remains unaffected," he said.

But the inability of the Iraqi soldiers to prevent looting in one of Iraq's calmest provinces, as well as the reported mutiny of a local army brigade, left doubts about whether U.S.-led forces will be able to hand over security to the Iraqi government anytime soon.

"Obviously this raises questions about the effectiveness of the Iraqi security forces," Christopher Preble, director of foreign policy studies at the Cato Institute, said in a telephone interview from Washington. "What progress has been made in the past three years in terms of standing up an Iraqi security force for taking over the country when the United States leaves?"

The looting turned violent at noon when individuals in the mob shot at the base, Burbridge said. The Iraqi troops asked the province's governor for permission to return fire, a decision the British military highlighted as evidence of the security force's training.

"It demonstrated that they understand the importance of civilian primacy, that the government, and not the military, is in charge," Burbridge said.