BAGHDAD (Reuters) - A 24-year-old military policeman will face a public court martial in Baghdad next week, the first of seven American soldiers to be tried on charges of abusing Iraqi prisoners, a U.S. military spokesman said Sunday.

Stung by photographs of humiliation that have hardened Arab anger at the United States, the army promised full media access when Specialist Jeremy Sivits goes on trial on May 19, but it was unclear if the court hearings would be televised.

"It is not our intention to hide anything," Brigadier General Mark Kimmitt told a news conference, though he has insisted there would be no "show trial."

Sivits, who faces three charges, including one of maltreating detainees, is one of seven military police to be charged with abusing prisoners in Baghdad's Abu Ghraib prison, where Saddam Hussein's torturers tormented thousands of Iraqis.

The case was opened in January but blew up into a major scandal 10 days ago when a U.S. television station published photographs showing grinning soldiers at Abu Ghraib with naked and hooded Iraqis in sexually humiliating postures. U.S. media say Sivits may have been among those who took the photographs.

The Washington Post quoted a Pentagon official Sunday as saying that more shocking images, including video and featuring "live-action abuse," could be released soon.

Despite new assurances from President Bush that the ill-treatment was the "wrongdoing of a few" -- implicitly the seven facing criminal charges and seven others already disciplined -- evidence has mounted of widespread abuses which have fueled anger among Iraqis at continued U.S. occupation.

BOMBS AND BULLETS

Violence also continues to trouble the run-up to a planned handover of sovereignty to Iraqis on June 30.

An explosion at a crowded market in Baghdad Sunday killed at least three Iraqis and wounded nine, including six policemen. Hospital staff had said earlier that seven people died. Three Iraqi policemen, two civilians and a guerrilla fighter were also killed in a shooting incident in Baghdad, Kimmitt said.

There were more scattered clashes between troops and the Mehdi Army militia loyal to Shi'ite cleric Moqtada al-Sadr.

Kimmitt said 18 militiamen were killed in the Shi'ite Sadr City stronghold in Baghdad Sunday. It was not possible to verify the casualty toll, but witnesses did see exchanges of fire, including mortar rounds. Saturday evening, U.S. troops, backed by tanks, raided Sadr's local office and arrested several aides, one of whom Kimmitt described as a financier.

Around Sadr's main stronghold in the holy city of Najaf, south of Baghdad, U.S. tanks opened fire from a base on the edge of the city after taking mortar rounds from suspected Sadr fighters. Several buildings were set on fire and hospital staff said at least three people were killed.

Further south, there was sporadic fighting between the Mehdi Army and British troops in Basra, where a British military spokesman said three soldiers were wounded in a grenade attack.

He said British troops came under mortar fire overnight in the town of Amara, but denied a report of a British air strike.

Mehdi Army fighters patrolled some streets in Basra but the city was generally calm a day after they fought running battles with British troops in the city.

The U.S. military has stepped up operations against Sadr in recent days, cracking down on the uprising the cleric launched against the U.S.-led occupation a month ago across the south.

Spurred on by rival Shi'ite leaders exasperated by the young firebrand, troops have reasserted control in many areas but not the holy sites in Najaf, where Sadr himself has taken refuge.

POLITICAL FALLOUT

Elsewhere, one U.S. soldier was killed and another wounded in a mortar attack on a military base in the northern Iraqi city of Mosul Saturday, a U.S. military statement said Sunday.

The death took to 559 the number of U.S. military personnel killed in action in Iraq since the invasion of the oil-rich country 14 months ago. The killing of 129 U.S. troops last month alone, made April the bloodiest month of the war.

The bloodshed and dismay among Iraqis and Americans at the torture and murder of prisoners by U.S. soldiers has not helped Bush's task in justifying his Iraq campaign to voters.

The most recent Gallup poll showed his approval rating on Iraq had fallen by almost a third to 42 percent since January.

His vice president came to the aid of Rumsfeld after Bush's presidential challenger John Kerry called for his resignation.