BAGHDAD — Shiite militants ambushed a U.S. patrol in Baghdad's embattled Sadr City district today and more than two dozen people were killed in the fighting, a U.S. military spokesman and Iraqi officials said. Six American soldiers were wounded.

The clashes broke out at 9:30 a.m. after U.S. troops were attacked with rocket-propelled grenades and machine guns, spokesman Lt. Col. Steve Stover said. As the troops were leaving the area, a vehicle was hit with two roadside bombs, Stover said.

Officials at the Imam Ali and al-Sadr general hospitals said about 25 people had died, with several dozen wounded. The officials who spoke on condition of anonymity because they are not authorized to release the information, said most of the victims were civilians.

Stover said U.S. forces targeted gunmen in the area with rockets fired from a guided multiple-launch rocket system, which fires high-explosive warheads weighing 200 pounds. He said 28 extremists were killed.

"We have every right to defend ourselves," he said. "The problem is they're using houses, rooftops and alleyways (as cover)."

Earlier Tuesday, eight people were killed and 67 wounded in the sprawling eastern district that is home to 2.5 million residents. Shiite militiamen and U.S. and Iraqi forces have been locked in increasingly violent street battles there during the past month.

A showdown between the Iraqi government and the Mahdi Army militia — led by anti-American cleric Muqtada al-Sadr — has increasingly drawn U.S. forces into battle.

Tuesday's attack occurred along a road on which the U.S. military is putting up a concrete barrier to try to cut off the militants' ability to move freely into the rest of Baghdad and hamper their ability to fire rockets and mortars at the heavily fortified Green Zone that houses Iraq's government and many foreign embassies.

AP Television News footage showed children running for cover behind blast walls amid gunshots. Men helped carry several blood-soaked injured people onto stretchers to a local emergency hospital. Outside the hospital, the dead were placed inside plain wooden coffins.

Also in Baghdad, a senior government official was killed in a roadside bombing in the north of the city.

Dhia Jodi Jaber, director general at the Ministry of Labor and Social Affairs, was hit by a roadside bomb as he left his home on Tuesday morning, the ministry's spokesman Abdullah al-Lami said.

Insurgents frequently target governmental officials and institutions in a bid to disrupt the government's work.

In the southern city of Basra, where the government began its crackdown on Shiite militias on March 25, Iraqi military commander Lt. Gen. Mohan al-Fireji announced the discovery of a huge weapons cache containing roadside bombs, mortar launchers and Iranian-made weapons.

More details on the amount of weapons or how authorities knew they were Iranian-made were not immediately available.

Meanwhile, the trial of Tariq Aziz, one of Saddam Hussein's best-known lieutenants, opened Tuesday in Baghdad.

Aziz is one of eight defendants facing charges in a case dating back to 1992 when the government executed 42 merchants for war-profiteering. Others include Saddam's half brother and the dictator's cousin known as "Chemical Ali," who faces a pending death sentence in another case.

Aziz has denied the accusations, his Italian lawyer said in a statement Tuesday.

Elsewhere, a female suicide bomber blew herself up at a bus stop near Muqdadiyah, about 60 miles north of Baghdad, killing one and wounding five people, police said.

In other developments, the Iraqi defense ministry said Serbia had agreed to write off $3 billion in Iraq's foreign debt.

Serbia's move comes after an international conference last week in Kuwait at which Prime Minister Nouri al-Maliki and Secretary of State Condoleezza Rice unsuccessfully pressed Saudi Arabia and other Gulf states to forgive Iraq's debts as a sign of support for Iraq's government.

Iraq harbors at least $67 billion in foreign debt — the vast majority of it owed to Saudi Arabia, Kuwait, the United Arab Emirates and Qatar.