A rash of bombings and skirmishes killed at least 13 Iraqis, a U.S. soldier and an Estonian soldier Monday, according to reports from around the country. Meanwhile, several hundred Iraqis staged a street demonstration in Baghdad to demand the release of Margaret Hassan, the veteran aid worker who was kidnapped last week.

Three Iraqi civilians were killed on a central Baghdad street when explosives apparently hidden in a parked car exploded beside an Australian military convoy. The force of the 8 a.m. blast, which occurred near the Australian Embassy, knocked an armored vehicle off the pavement. It was the first attack directed against an Australian force that protects the country's diplomats in Baghdad. Three Australian troops and six Iraqis were wounded.

In western Baghdad, a roadside bomb killed one U.S. soldier and wounded five, the U.S. military said.

The Estonian was killed when an explosive charge detonated beneath a convoy in western Baghdad. He was the second soldier from the Baltic country to die in Iraq this year. Estonia maintains 45 troops here.

Fighting between U.S. forces and insurgents in Ramadi, the capital of Anbar province, west of Baghdad, killed five civilians, according to a hospital director quoted by the Reuters news agency.

A bomb planted in the vehicle of a tribal leader in the northern city of Mosul killed three people, including the unidentified sheik, when it detonated outside the downtown headquarters of the provincial government, according to news service reports. A second car bombing targeted the commander of the city's Facilities Protection Service, which guards government buildings. He survived, but three guards were wounded.

News services reported two other civilians killed in insurgent attacks: a man struck by shrapnel from mortar fire apparently aimed at an Iraqi National Guard base north of Baghdad, and a farm worker killed when a roadside bomb apparently meant for a U.S. patrol exploded 50 miles southwest of Kirkuk, also in the north.

In Khaldiya, about 12 miles west of Fallujah, a suicide bomber steered a sedan into a convoy of six U.S. military vehicles.

"The Americans warned the driver not to be close, but he did not care," said Laith Mohammed, 23, a laborer who witnessed the incident. "We immediately thought he will blow up the car. He had a beard. The Americans started shooting, but he drove fast and hit them.

"I saw some civilians driving, and some of them were wounded by shrapnel and some of them by the shooting of the Americans," said Mohammed. There was no immediate report of casualties from the military.

In Fallujah, which insurgents have held since April, the body of the leader of a radical group was pulled from rubble left by a U.S. airstrike. Abu Thar Qatary was identified by locals as a leader of the Ansar al-Sunna Army, a group that has posted several videos of beheadings on the Internet and asserted responsibility for suicide attacks.

The largely Kurdish group is one of several successors to Ansar al-Islam, which U.S. and allied Kurdish forces routed from a stronghold in northern Iraq at the start of the war. Ansar al-Sunna operates mostly in Mosul and other northern cities but has sent fighters to Fallujah in anticipation of a U.S. assault on the city, residents said.

In Najaf, the southern city badly damaged by fighting between U.S. forces and a Shiite militia in August, U.S. Marines have paid more than $1.9 million in compensation for lives lost and property damaged in the hostilities, according to the Marines. The money has been distributed to 2,660 residents so far.

"Now that Najaf is secure, we're working around the clock to get this city up and running again," Col. Anthony M. Haslam, commander of the 11th Marine Expeditionary Unit, said in a statement. "These payments are one way we are showing goodwill and building trust with the locals."

The kidnapping of Hassan, the aid worker, has caused an outcry in Iraq, where she has spent 30 years working in social welfare programs. Last week her captors released video footage of her pleading to Britain's prime minister, Tony Blair, for the withdrawal of British forces from Iraq.

"We love her. She built us a hospital," said Ahmed Jabir, who spoke from his wheelchair at a rally attended by several hundred Iraqis, many of them disabled, outside the Baghdad office of CARE International, where Hassan worked. A banner read: "Please release Margaret Hassan who has helped us."

"If it wasn't for her," Jabir told Reuters, "we would probably have died."

Australian troops secure the site of a blast that killed three Iraqis and injured three Australian soldiers in central Baghdad. Meanwhile in a western section of the capital, a roadside bomb killed one U.S. soldier and wounded five.