Updated

More than 500 Iraqi men have joined the police in restive Anbar province — a focal point of the Sunni Arab insurgency — in the most successful recruiting drive in the region by U.S. and Iraqi forces, the U.S. military said Tuesday.

Also Tuesday, two people were killed in a bomb explosion in Baghdad and two people were killed during clashes between British forces and gunmen in the southern city of Amarah, police said.

U.S. Marines screened thousands of applicants earlier this month in various regions along the western Euphrates River valley before shortlisting the recruits for the Anbar police force, said a statement by the U.S. command.

CountryWatch: Iraq

Most American deaths this month have been in Anbar province west of Baghdad, where support for the Sunni Arab insurgency runs deep. The latest casualties in Anbar were two Marines and a sailor who were killed in combat Sunday. All three belonged to the Regimental Combat Team 7, which conducted the three-day police recruitment.

Maj. Lowell Rector, head of the police transition team for RCT-7, called the recruiting drive the most successful the U.S. and Iraqi forces had launched since the U.S.-led invasion of Iraq in March 2003, according to the statement.

He attributed the success to consistent pay for recruits and better police equipment.

RCT-7 is the U.S. military unit responsible for providing security and training Iraqi security forces in Anbar, an area of more than 30,000 square miles stretching from the Jordanian and Syrian borders to Hit, a city 85 miles west of Baghdad.

The situation in Anbar, with its heavily Sunni population, is a barometer for Iraq's entire Sunni Arab minority, which lost its favored position to the majority Shiites and the Kurds when Saddam Hussein's regime collapsed in 2003.

Many local Sunni leaders in Anbar province remain convinced that they can regain power in Baghdad through the armed insurgency.

The majority of Iraqi security force personnel are Shiite or Kurdish — while young Sunni Arabs make up much of the insurgency. The Americans would like to redress the imbalance and bring more Sunnis into the ranks.

But efforts to recruit more Anbar Sunnis into the army have thus far faltered, either because of intimidation by insurgents or genuine support for their cause.

The recruitment of more than 500 police cadets is a significant achievement in the American goal, but desertion rate remains high among the Iraqi army and police force, often because the foot soldiers don't get paid in time or get fatigued by the ongoing fighting.

If all 500 new applicants stay with the force after the training period, which last from eight to 10 weeks, Anbar will have more than 2,200 police officers in uniform, the statement said.

The Sunni insurgency and the Shiite-Sunni sectarian conflict wracking Baghdad and surrounding areas are the main challenges for the unity government, which some fear could lead the country to civil war.

The violence claimed about 3,500 lives in July, the highest monthly death toll since the U.S. led invasion in March 2003. More than 2,600 members of the U.S. military have also died in Iraq since the invasion.

Still, the Ministry of Defense said in a statement that terrorist activities have declined by 70 percent since U.S. and Iraqi troops launched a revamped security crackdown in the capital on Aug. 14 with a reinforcement of 12,000 troops. It said 14 terrorists and 439 suspects have been detained since the launch of the operation.

On Tuesday, two civilians were killed in crossfire during an exchange of fire between British forces and militiamen in Amarah, 180 miles southeast of Baghdad, said the region's governor, Adil Mehodar al-Maliki.

Elsewhere, a bomb hidden in a bag exploded on a street in Tayaran Square in central Baghdad on Tuesday, killing two civilians and wounding nine, said police Lt. Bilal Ali. A Shiite engineer was shot dead while he was in his car in Baghdad, said police 1st Lt. Mitham Abdul-Razaq.