Militants: Captured U.S. Marine beheaded
A minibus burns after rocket strikes in Baghdad.
Saddam Hussein appears in court to hear charges.
The new Iraqi regime faces a number of security challenges.
DUBAI, United Arab Emirates (CNN) -- Militants in Iraq claimed Saturday to have beheaded a U.S. Marine who disappeared from his post last month, but neither the military nor news organizations could confirm the report posted on three Islamic web sites.
A message -- purportedly from Abdullah al Hasan ben Mahmoud, who claims to be emir of a group that calls itself Ansar al-Sunna -- addressed President Bush when describing the alleged fate of Cpl. Wassef Ali Hassoun, a Marine translator of Lebanese descent
"We inform you, your excellency, your military officer who is originally Lebanese has been beheaded. And you will see that with your own eyes," the statement said.
The militants said a video will be released of the Marine and another hostage, purportedly an American.
Hassoun, who was trained as a truck driver but worked as a translator, was reported missing June 20 when he did not report for duty at his base in Iraq. He was last seen June 19.
The slangy, sarcastic message said the Marine had "a relation with an Arab woman and that's how he was pulled out of the base."
"We'll be showing very soon a video of how he was arrested and as promised finally how he was beheaded," the statement said. "Pull your military and you'll be safe."
On June 27, the Arabic-language network Al-Jazeera broadcast video of a man identified as Hassoun surrounded by armed men.
His captors showed his Marine identification papers, and one of them brandished a sword above his head.
On the tape, a speaker said the man was lured from his base and captured, and his captors threatened to kill him unless U.S. military authorities released Iraqi prisoners.
Weapons factory shut down
U.S. troops discovered weapons factories and cars rigged to explode in a two-day operation in southern Baghdad, which also led to the arrest of key suspects in other attacks, the U.S.-led coalition said Saturday.
In the operation that discovered the weapons factories, 1st Cavalry Division soldiers found four potential car bombs at "various stages of completion" at a site where they also found more than 12 million Iraqi dinar ($8,200), documents and other bomb-making apparatus, according to a coalition news release.
Three people were detained there.
Also Saturday, a bomb killed six Iraqi National Guard members at an oil storage facility in a town south of Baghdad, according to police, and a U.S. Marine died after fighting in Anbar province, the coalition said.
In the operation to uncover weapons, the soldiers found rocket-propelled grenade launchers and 50 pounds of C4 plastic explosives -- and detained 30 people, who led them to eight other sites that netted more weapons and 18 other suspects.
"The detainees are allegedly part of a cell responsible for placing [improvised explosive devices] that have killed two soldiers in the area," the news release said. "The soldiers believe they have captured the financier, the explosive device manufacturer, the spotter and the triggerman."
Progress in halting the widespread instability in Iraq will come in tandem with the interim Iraqi government's maturity, said Foreign Minister Hoshyar Zebari, delivering comments Saturday in Baghdad at a news conference with Romania's foreign minister.
"The security challenge is related to the progress and advance we make in the political process," Zebari said.
"The more we move forward, the more people of Iraq believe this transfer is real, is genuine, it's credible, and the Iraqis are in charge, are in the driving seat. This is the main challenge."
The Marine who died Saturday was a member of the 1st Marine Expeditionary Force and had been wounded in action Friday in the province west of Baghdad.
The Marine was the fourth to die in the province since Thursday. The death brings the number of fatalities of U.S. troops since the war began to 864 -- 642 in hostile action and 222 in nonhostile activity, according to the U.S. military.
Violence in south
The six Iraqi National Guard members died in an explosion south of Baghdad at an oil-storage installation, an Iraqi police official said. Five others were wounded.
The Guard members had been stationed at the facility, watching over it at the time.
It happened in Latifiyah, according to a police official at the nearby town of Mahmoudiyah, 20 miles south of the capital. The bomb detonated during a changing of the guards.
In Basra, a roadside bomb detonated Saturday morning as a British military convoy passed by, wounding a British soldier and damaging two vehicles, according to the Multinational Division's press office.
CNN's Guillaume Debre, Brent Sadler and Alphonso Van Marsh contributed to this report.