BAGHDAD -- Britain froze plans Tuesday to withdraw about 1,500 soldiers this spring after the faltering effort to drive Shiite militias from Basra, Iraq, raised doubts whether the Iraqis are capable of maintaining security in oil-rich southern Iraq.
The British decision was announced in London one week before the top U.S. commander in Iraq appears before Congress to offer his recommendation on how fast America should draw down its own forces.
Defense Secretary Robert Gates said Monday in Copenhagen, Denmark, that last week's violence in Shiite areas had not changed American plans to withdraw more combat forces by July.
But second thoughts about Iraqi security capabilities emerged as Iraq's government reported a 50 percent rise in the number of people killed in March over the previous month.
Much of the increase was a result of the fighting between Iraqi government forces and Shiite militiamen in the southern city of Basra. The conflict quickly spread, engulfing Baghdad and major cities throughout the Shiite south.
Britain had planned to draw down its 4,000-strong military force in southern Iraq to 2,500 over the next few months, handing over more security responsibility to the Iraqis.
In the wake of the Basra fighting, however, Defense Secretary Des Browne told the House of Commons that "it is prudent that we pause any further reductions while the current situation is unfolding."
"At this stage we intend to keep our forces at their current levels of around 4,000 as we work with our coalition partners and with the Iraqis to assess future requirements," Browne said, promising to update lawmakers later this month.
Browne offered no criticism of the Iraqi effort in Basra, launched March 25 to regain control of the country's second-largest city from Shiite militias and criminal gangs which have effectively ruled the streets for nearly three years.
The operation faltered in the face of fierce resistance from the Mahdi Army of anti-American Shiite cleric Muqtada al-Sadr, forcing the Iraqi military to turn to U.S. jets and British tanks and artillery to try to dislodge the gunmen from their strongholds.
Britain's opposition Conservative party defense spokesman, Liam Fox, complained that the Iraqis had not fully consulted their coalition partners before launching the operation.
Fox said it was "not acceptable for us to end up mopping up if we don't have a say in what operations are being carried out and how they are being carried out."
Iraqi officials have acknowledged they underestimated the fury of the militia resistance, which included rocket and mortar attacks against the U.S.-controlled Green Zone in Baghdad and armed assaults against government and political party offices throughout the south.
Prime Minister Nouri al-Maliki, a Shiite, flew to Basra last week and took personal command of the crackdown, promising he would remain in the city for "a decisive and final battle" to crush the militias.
Fighting eased after al-Sadr called his fighters off the streets Sunday under a deal brokered by Iran. But al-Sadr's fighters refused to surrender their weapons -- a development which left the cleric in a position of power and al-Maliki politically battered.
Al-Maliki returned Tuesday to Baghdad, declaring the operation a success although several Basra neighborhoods appeared to remain under militia control. Al-Sadr, meanwhile, thanked his fighters for "defending your people, your land and your honor."
U.S. and Iraqi officials have insisted the target of the crackdown was not the Sadrist political movement but criminals and renegade militias. But the Sadrists believed the operation was aimed at weakening their movement before provincial elections this fall.
The recent carnage threatened to reverse the security gains achieved in Iraq since President Bush ordered 30,000 U.S. reinforcements to Iraq early last year.
Figures compiled by the ministries of health, interior and defense showed that at least 1,720 people were killed in politically motivated violence in March. That was up sharply from the 953 figure for February.
Figures tabulated by The Associated Press from police and U.S. military reports put the March death toll as of Monday at 1,247 -- nearly double the February figure and the biggest monthly toll since August, when 1,956 people died violently.
The latest bloodshed and Iraqi military capabilities are expected to draw attention next week when the top U.S. commander in Iraq, Gen. David Petraeus, briefs Congress about prospects for further troop cuts.
The Pentagon is expected to reduce U.S. troop levels from about 158,00 to about 140,000 by the end of July.
Petraeus has repeatedly warned that security gains are fragile and has already indicated that he wants a "period of assessment" for at least several weeks after July before deciding on the timing of further withdrawals.
Sporadic fighting continued Tuesday in Baghdad and Basra, but the cities were generally calm. Several rounds were fired late Tuesday toward the Green Zone, but there were no reports of damage or casualties.
Before dawn Tuesday, a U.S. helicopter fired a missile at gunmen attacking American ground forces in the Baghdad militia stronghold of Sadr City, killing six militants, the U.S. military said. Iraqi police and witnesses said three civilians were killed in the strike.
The Iraqi Red Crescent Society, the Muslim world's equivalent of the Red Cross, complained Tuesday that U.S. forces prevented its relief convoy from getting into Sadr City.
A Red Crescent official, Ammar Khalid Saied, told AP Television News that his convoy tried to deliver food, medical supplies and water to Sadr City but could not get permission from the U.S. to enter the area.
A U.S. spokesman, Maj. Mark Cheadle, said American soldiers were not blocking humanitarian convoys but were checking vehicles because "criminal and terrorist groups" sometimes hijacked them to transport weapons and fighters.
Elsewhere, police and Mahdi militiamen exchanged gunfire early Tuesday in Nasiriyah, police and residents said. Three policemen were killed, and a desk to dawn curfew was imposed on the surrounding province, officials said.
Associated Press correspondents David Stringer and Tariq Panja in London contributed to this report.