Nine U.S. Marines were killed and nine wounded in violence on Saturday, the deadliest day for American forces in Iraq in almost six months. At least 25 Iraqi civilians were killed by a car bomb, an insurgent rocket and what news reports called reckless fire by Iraqi security forces.

Eight of the Marine deaths and the nine injuries occurred when a car bomb detonated next to a truck southwest of Baghdad, Maj. Clark Watson of the 1st Marine Expeditionary Force told the Associated Press. The attack took place in Anbar province, which extends west from the capital to the borders of Syria and Jordan. A ninth Marine was also killed Saturday, officials, who gave no other details, said.

Anbar province includes the insurgent stronghold of Fallujah, against which U.S. forces are preparing a major offensive. On Saturday, they unleashed an artillery barrage and an airstrike on targets in the city. U.S. military patrols elsewhere in Anbar are frequently ambushed by roadside bombs and, increasingly, cars laden with explosives.

The headless body of a Japanese backpacker who was abducted in the capital earlier this week was recovered wrapped in an American flag in Baghdad. The Japanese government confirmed through fingerprints that the corpse was that of Shosei Koda, 24, the Associated Press reported. Koda was threatened with beheading by a group affiliated with Abu Musab Zarqawi, a Jordanian-born insurgent leader in Iraq.

Hours after Koda's body was found Saturday, a Polish woman held by militants since last week pleaded for her life and asked Poland to remove its troops from Iraq in a video aired by al-Jazeera television. Teresa Borcz Khalifa, 54, who holds dual Polish-Iraqi citizenship, sat in front of a banner with the militant group's name, the Abu Bakr al-Siddiq Fundamentalist Brigades.

In Baghdad, seven people were killed and 17 wounded, some seriously, when a car bomb exploded outside the office of al-Arabiya, a satellite news channel. The thunderous blast, which occurred while many members of the station's staff were finishing a meeting in the front room, was the worst attack on a news organization in Iraq.

"We cannot supply you with any footage because the office and the sets were all destroyed," an al-Arabiya reporter, Najwa Qasim, said on the air a few minutes after the attack. Two burned bodies lay at her feet and firefighters poured water on flaming parked cars as she spoke.

Another reporter cautioned that the bomb might have been intended for a different building in the same area of the prosperous Mansour neighborhood, where government buildings and the homes of prominent politicians are also located.

But minutes after the blast, a group calling itself the 1920 Revolution Brigades asserted responsibility for the attack in a message posted on the Internet. The group called al-Arabiya a "treacherous network" and "Americanized spies speaking in Arabic tongue."

The group had been unknown until earlier in the day, when it released a videotape of a kidnapped Sudanese who had been working as an interpreter for a U.S. contractor.

Employees of the network, which is based in Dubai but owned by Saudi investors, have paid a steep price for reporting on the escalating violence in Iraq. Two of its journalists were fatally shot by U.S. soldiers in March at a checkpoint in Baghdad, in what the military called a tragic accident. Another correspondent was fatally wounded by fire from a U.S. helicopter in September while doing a report alongside a disabled armored vehicle in Baghdad.

Al-Arabiya remained in Iraq after a rival Arabic language news network based in Qatar, al-Jazeera, was officially barred by Iraq's interim government on the grounds that it promoted the insurgency.

In the smoky aftermath of the bombing Saturday, two men debated whether al-Arabiya had so distanced itself from the insurgency that it had become a target for attack. "I noticed lately they started using the word 'dead' instead of 'martyr' for the people killed at Fallujah, for example," said one of the men, who gave his name only as Ahmed.

At least 14 people were killed south of the capital when Iraqi security forces opened fire on a busy street. The Iraqi forces arrived in the area and began firing on bystanders just after a U.S. convoy was attacked by as many as three roadside bombs, witnesses said according to the Associated Press.

The guardsmen sprayed fire into three minibuses and randomly threw grenades, according to the report. A cameraman for Associated Press Television News reported seeing 18 bodies. Witnesses said the guardsmen also broke into a nearby mosque and detained a cleric and two guards, the AP reported.

The incident occurred in Haswah, a town 25 miles south of Baghdad, in an area where insurgents have carried out ambushes and kidnappings. Two days earlier in the nearby town of Yusufiya, a father and son were found dead in the middle of a road, according to the military. At their feet were their graduation certificates from the Iraqi police academy.

In Baghdad's Jadariya neighborhood, a rocket fired by insurgents landed on a house, killing at least four members of a family inside, witnesses said. The missile was apparently intended for the nearby Ministry of Interior building, which is frequently targeted by insurgents launching missiles from the south.

Meanwhile, U.S. forces pressed insurgents in Anbar's two largest cities. In Fallujah, which has been held by local and foreign fighters since April, Marines ramped up for a threatened offensive intended to return control of the city of 300,000 to Iraq's interim government in time for elections planned for January. Warplanes crossed the skies above the city, as the booms of artillery shells shook the ground at a Marine outpost near Fallujah. The engagement lasted more than an hour.

Fighting was also reported in Ramadi, 30 miles west of Fallujah, which U.S. commanders have also threatened to re-take by force. A mortar attack Saturday on a government complex killed two Iraqi police officers and wounded four, the Reuters news agency reported.

Correspondent Jackie Spinner near Fallujah and special correspondents Naseer Nouri and Bassam Sebti in Baghdad contributed to this report.

A convoy of trucks carrying bottled water for U.S. troops burns after being attacked by insurgents in the northern Iraqi city of Mosul. Two drivers were killed and two others were kidnapped.A U.S. Marine mans a machine gun atop a Humvee on patrol outside Fallujah, 35 miles west of Baghdad, which has been held by insurgents since April. Najwa Qasim, a correspondent for al-Arabiya, speaks to U.S. soldiers after a car bomb exploded near the Baghdad bureau of the satellite news channel. Iraqis walk through the remains of a house destroyed by an American airstrike in Fallujah. U.S. forces attacked suspected insurgent bases in preparation for a possible offensive against the city.