Three suicide bombers attacked the headquarters of the 82nd Airborne Division west of Baghdad on Thursday, causing injuries but no US deaths. It was the third suicide attack on American troops this week.  

There were no US fatalities in any of the suicide attacks, indicating that massive defenses erected at American facilities are paying off.

The three Iraqis in the car died in Thursday's explosion, a military source said on condition of anonymity. The number of American soldiers hurt was not yet known.

The bombers who hit the Champion Base in Ramadi, 60 miles west of Baghdad, detonated their bomb just outside the gate, the source said, providing no other details.

The region around Ramadi and the nearby city of Fallujah is one of the most dangerous for coalition troops and sits in the so-called Sunni Triangle, where the majority of US deaths in hostile action have occurred since US President Bush declared an end to major fighting May 1.

On Tuesday, suicide bombers, one in a car and another on foot, blew themselves up at the gates of two US military bases, wounding at least 61 American soldiers but failing to inflict deadly casualties on the scale of recent attacks in Iraq.

Most of the soldiers were slightly hurt by debris and flying glass, indicating the defenses around US facilities -- sand barriers, high cement walls and numerous roadblocks leading to the entrances of bases -- were having an effect.

At the same time, the decision of the suicide bombers to continue testing US defenses reflected the tenacity of an enemy that seeks to undermine American resolve by inflicting mass casualties with a single strike.

Also Thursday, the military reported one US soldier drowned and another was missing after a patrol-boat accident on the Tigris River in Baghdad.

"The soldiers were conducting routine patrols on the Tigris River when one of the soldiers fell overboard, and the other soldier jumped in to save him," the US Central Command in Florida said in a statement.

The incident occurred Wednesday, and the drowned soldier from the US Army's 1st Armored Division was found Thursday morning, the statement said.

Also Thursday, US soldiers said an Apache helicopter that crash-landed near the northern city of Mosul might have been hit by ground fire while making a low pass over the area.

A military spokesman had insisted that the helicopter was forced to crash land on Wednesday because of mechanical failure and that the uninjured crew reported no ground fire. But a commander later said that he didn't know whether ground fire brought down the helicopter, from the 101st Airborne Division.

The Apache came down near a highway about 15 miles south of Mosul, Iraq's third-largest city, which has been the site of escalating anti-occupation resistance.

Troops guarding the site where the burned-out wreckage was still smoldering on Thursday morning said the chopper had been hit by enemy fire while flying over the area on a low-level patrol. They asked not to be identified.

"The helicopter was shot down," one said.

Brig. Gen. Frank Helmick of the 101st later said the cause of the crash was unclear.

"We don't know what happened," he said. "It could have been a mechanical failure but again, we are looking at all possibilities."

Mosul was the site of the deadliest incident so far involving US forces. On Nov. 17, two Black Hawk helicopters collided and crashed, killing 17 soldiers. Although military spokesmen initially insisted that the collision was the result of an accident, officers have since acknowledged that ground fire was the likely cause.

Also Thursday, Ghazi al-Talabani, director of the Northern Field Protection Force, which guards pipelines in northern Iraq, said an explosion set a pipeline ablaze, forcing officials to halt the flow.

He said the pipeline links the Beiji refinery in northern Iraq with the al-Doura refinery near Baghdad. A complex grid of pipelines move oil and natural gas throughout the region, and it was unclear how major the pipeline was.

If it is confirmed that the Apache was shot down, it would be the sixth military helicopter downed in six weeks.

Separately, US forces in Tikrit -- Saddam Hussein's hometown north of Baghdad -- arrested three men believed to be leaders of a guerrilla cell responsible for attacks against American troops and Iraqi civilians. The raiders seized weapons and bomb-making gear, a US commander said Thursday.

"They are suspected members of a local (guerrilla) organization called Mohammed's Army and they received funding from the elements of the former regime," said Lt. Col. Steve Russell, commander of the 1st Battalion, 22nd Infantry Regiment of the 4th Infantry Division.

Russell's unit arrested the men after storming two houses in Tikrit.

Also in Mosul, two US soldiers were killed Wednesday and four injured in two separate attacks. The predominantly Sunni Muslim city is home to many former soldiers and Saddam loyalists.

In Samarra, another volatile city 60 miles north of Baghdad, two members of the US-led paramilitary Civil Defense Corps were killed overnight by unidentified gunmen while on patrol, witnesses said Thursday.

In Baghdad, guerrillas struck a US Air Force C-17 transport plane on takeoff with a ground-fired missile, forcing it to return to the capital's international airport, a senior Pentagon official said Wednesday.

(China Daily December 12, 2003)