Baghdad, Iraq ? Marines fought insurgents Wednesday in Ramadi and Fallujah, and combat flared in six other cities as a rebellion led by an upstart Shiite cleric continued into its fourth day.

One U.S. soldier was reported killed Wednesday, and coalition soldiers from Ukraine abandoned Al Kut in central Iraq, leaving it to soldiers from Muqtada al Sadr’s Mahdi Army. Sadr’s militia was already in control of Najaf, the holy Shiite city.

U.S. Marines, while nominally in control of Fallujah and Ramadi, continued to face opposition. Witnesses in Ramadi said Marines who’d been fighting for 24 hours straight paused only to refill ammunition. Insurgents were getting the worst of it, as Marine snipers picked them off one by one.

In Fallujah, U.S. bombs struck near a mosque. U.S. officials said one person was killed, but a BBC report placed the death toll at 40.

The death toll for coalition forces in the last two days of fighting stood at 34, including 12 Marines who died Tuesday in Ramadi. Ten of those Marines were from a single company. Three Marines have died in Fallujah since Monday, U.S. officials said.

The Iraqi death toll was much higher, perhaps more than 500. Marine engineers patrolling near Ramadi on Wednesday reported coming across a mass grave containing up to 350 bodies of Iraqis who appeared to have been killed in the fighting. It wasn’t clear whether the bodies belonged to combatants, civilians or both.

Shiites, Sunnis unite

Meanwhile, evidence continued to build that rival Shiite and Sunni Muslims have set aside centuries of hatred and joined to fight their common enemy, the United States. One coalition official said that such a scenario, if it were to develop, would make Iraqi occupation “significantly more dangerous.” A Shiite leader in Baghdad’s Sadr City, the sprawling Shiite enclave, told Knight Ridder that Sunnis and Shiites had been talking for weeks about how to join forces against the U.S.-led coalition.

Baghdad remained a largely empty city, as residents, apparently fearing more violence, stayed inside their homes. Schools and businesses were closed, and streets were devoid of the city’s usually dense traffic.

Rumors, unconfirmed and unconfirmable, heightened the tension: Those involved in the insurgency said Sunnis, Shiites and even Palestinians would gather today for a war summit in Sadr City.

An Iraqi Special Forces soldier yells at other soldiers while they and Marines clear an apartment building on the northwest side of Fallujah, Iraq. The campaign to locate insurgents in the city was conducted Wednesday.

“The Sunni people, the Shiite people, we share the same God, the same suffering under the Americans and the same goal, to end the occupation of Iraq,” said Said Ammer al Husainie, the Mahdi Army leader in Sadr City. “We have been working together, and will continue to work together, to see that our aims are met.

“We would be willing to see a peaceful solution. We do not like all the bloodshed,” he added. “But we have no trust left for the Americans. They have proven themselves again and again to be liars.”

Al Sadr ‘a stupid little man’

Coalition officials at all levels continued to scoff at Sadr and his forces. One adviser in the coalition legal office privately called al Sadr “a stupid little man.” He said it was unlikely he had formed a coalition with Sunnis and Palestinians.

“He has a few followers in Sadr City and some down south in Basra,” the official said. “Other than that, most Iraqis despise the man. He claims more followers than he has to make himself feel big.”

Those comments echoed the public refrain. “The vast majority of Iraqis reject his message of violence,” said U.S. Army Brig. Gen. Mark Kimmitt.

In Washington, Secretary of Defense Donald Rumsfeld called the violence the work of “thugs and assassins” who don’t represent the majority of Iraqis.

Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, described the insurgents in Ramadi and Fallujah as “former regime elements” consisting of “Baathists, Iraqi extremists, extremists from outside” Iraq.

Grim signs

But there were some signs that the Shiite-Sunni alliance might be more than imaginary:

• The BBC reported that Shiite fighters had entered a Sunni mosque Monday, recruiting volunteers to donate blood for the resistance. Once recruited, the volunteers “together agreed on a wide-range attack in the neighborhood on the Americans,” the BBC reported.
• In Ramadi, a traditional Sunni stronghold, witnesses said Marines were fighting soldiers who were dressed like members of Mahdi Army.
• In southern and central Baghdad, traditional Sunni neighborhoods, pro-Sadr posters and literature were widely circulated.

Kimmitt acknowledged that “we have concern” about Sadr’s control of Najaf. But he said coalition forces were firmly in control of Ramadi and Sadr City and that Sadr’s followers controlled no government buildings or police stations in Sadr City.