The latest ambush, near Mahaweel, about 35 miles south of Baghdad, also wounded two pilgrims, police Capt. Muthana al-Furati said. Attacks on pilgrims Monday killed four people, including two police officers guarding pilgrims.

Roads across Iraq were crowded with Shiites heading to the holy city of Karbala to celebrate the al-Arbaeen festival today. The holiday marks the end of a 40-day mourning period for one of the Shiites’ most important saints, the grandson of Prophet Muhammad, Imam Hussein, who was killed in a seventh-century battle.

Wearing white coffin shrouds signaling their readiness for martyrdom, tens of thousands of supporters of Shiite cleric Muq-tada al-Sadr, who has led uprisings against the U.S.-led forces in Iraq last year, paraded through the streets of Karbala.

’’We’re the Mahdi Army. We came to you, oh Hussein,’’ they chanted while snaking through the city. Some held photos of al-Sadr and waved swords, and others beat their chests with their fists in a sign of mourning.

Also Wednesday, Al-Jazeera satellite television aired a tape said to show three kidnapped Romanian journalists and a fourth unidentified person, guns pointed at their heads. The station said the four were being held by an unidentified group and no demands were made. The tape’s authenticity could not be verified.

The tape appeared a day after Romania’s government, which has 800 soldiers in Iraq, said three journalists were abducted near their Baghdad hotel Monday. They were grabbed after interviewing interim Iraqi Prime Minister Ayad Allawi, officials said.

In northern Mosul, four insurgents opened fire at a U.S. checkpoint and were killed by soldiers, a police official said. The gunmen killed six Iraqis.

The U.S. military said it had no information on the clash, but said three suspected insurgents were killed in a clash in Mosul after soldiers stopped a taxi that exploded, injuring five soldiers.