Gunmen opened fire on the Spanish garrison near the holy city of Najaf (search) on Sunday during a huge demonstration by followers of an anti-American Shiite Muslim cleric. One American soldier, one Salvadoran soldier and at least 14 Iraqis died, and more than 130 people were wounded.

Two U.S. Marines died in violence in Anbar province (search), bringing to 600 the number of American service members killed in the war. Anbar is an enormous stretch of land reaching to the Jordanian and Syrian borders west of Baghdad that includes Fallujah, a city where four American civilians were slain on Wednesday.

North of the capital, a bomb killed three members of the Iraqi security forces. And in Kirkuk (search), also in the north, a car bomb exploded, killing three civilians and wounding two others, police said.

Later in Baghdad gunfire was heard in the center of the capital during a similar protest called by backers of the charismatic young cleric, Muqtada al-Sadr (search). There was no immediate word on casualties.

In Najaf, the shooting broke out after thousands of al-Sadr supporters gathered outside the Spanish garrison. A spokesman for the Spanish headquarters in nearby Diwaniyah, Commander Carlos Herradon, said attackers opened fire about noon.

The Spanish and Salvadoran soldiers fired back, and assailants later regrouped in three clusters outside the base. Shooting continued into the afternoon, he said.

Along with the two coalition soldiers killed, nine were wounded, the Spanish Defense Ministry said in the Spanish capital, Madrid.

The Salvadorans are under Spanish command as part of an international brigade that includes troops from Central America. No Spaniards were injured.

Spain has 1,300 troops stationed in Iraq, and the Central American contingent is of a similar size. Multiple train bombings in Madrid last month killed 191 people and have been blamed on Al Qaeda (search) linked terrorists who said they were punishing Spain for its alliance with the United States in Iraq and Afghanistan.

Spain's new government, elected just days after the bombing, has promised to make good on a pre-election promise to withdraw all Spanish troops from Iraq unless command for peacekeeping is turned over to the United Nations.

An official at Najaf General Hospital, Alaa Murtada, said seven bodies were brought to that facility. He said the hospital treated at least 90 people.

Witnesses saw four bodies at al-Zahraa Hospital and nurse Saad Abdel-Hussein said at least 30 people were injured, some seriously.

Three bodies and 10 injured people were brought to Sadr Educational Hospital in Najaf, said doctor Ra'ad al-Hadrawi.

The slain Iraqi soldiers were inside the Spanish base, according to witnesses.

The crowd was protesting the reported detention of an aide to al-Sadr, the 30-year-old cleric opposed to the U.S.-led occupation of Iraq.

Five thousand people marched to the Spanish garrison after hearing that Mustafa al-Yacoubi (search), a senior al-Sadr aide, had been detained.

Spanish troops in the area have said they had no information on al-Yacoubi's reported detention and said they did not take part in any such operation.

At headquarters of the U.S.-led coalition in Baghdad, authorities said al-Yacoubi had been detained. The senior offiical, speaking on condition of anonymity, would give no other details.

In central Baghdad's Firdaus Square, hundreds of al-Sadr supporters rallied to protest al-Yacoubi's reported arrest. Police fired warning shots during the demonstration, and at least two protesters were injured, witnesses said.

Also, residents of Sadr City, a mainly Shiite district in eastern Baghdad where support for al-Sadr is strong, stormed several police stations and the local council building, witnesses said.

Al-Sadr's office in Baghdad issued a statement later Sunday calling off street protests and saying the cleric would stage a sit-in at a mosque in the city of Kufa, which is near Najaf, where he has delivered fiery weekly sermons for months.

About 5,000 members of al-Sadr's self-styled militia, the al-Mahdi Army (search), paraded in Sadr City, a mainly Shiite district in eastern Baghdad, on Saturday.

Al-Sadr's weekly newspaper was shut by U.S. officials on March 28, prompting an angry response from his supporters.

Two U.S. Marines, both assigned to the 1st Marine Division, were killed as a result of separate "enemy action" in Anbar province on Saturday, the military said in a statement. One died the same day; the other died Sunday. The statement provided no other details.

A bomb exploded Sunday near a checkpoint in Samarra, about 60 miles north of Baghdad, that was manned by Iraqi Civil Defense Corps personnel, killing three and wounding one, workers at Samarra General Hospital said.

In the city of Baqouba, 30 miles northeast of Baghdad, a bomb exploded Sunday in the al-Rasool al-Adham Shiite mosque, damaging part of the building, but causing no casualties, said the mosque's caretaker Haider Yassin.

In southern Iraq on Sunday, rebels attacked an oil pipeline, rupturing it and setting the oil on fire, said Jamal Khalid, an official with the Southern Oil Company.

Firefighters were battling the blaze and expected to put it out within a few hours, he said. The fire will not affect oil exports, he added.

The pipeline links the southern city of Basra with the Persian Gulf port of Faw. Rebels have repeatedly attacked oil pipelines in Iraq.

The coalition announced Sunday the appointment of Ali Allawi, the interim trade minister, as the new defense minister and Mohammed al-Shehwani, a former Iraqi air force officer who fled from Iraq in 1990, to head the Iraqi National Intelligence Service.