BAGHDAD �?Helicopter gunships and fighter jets streaked across the desert sky Saturday as U.S. and Iraqi forces battled insurgents near the Syrian border, killing at least 50 militants in two massive offensives to stanch the flow of foreign fighters from Iraq's western neighbour.

The military reported the deaths of two U.S. soldiers, killed north of Baghdad during an attack as they were taking a captive to jail.

Intelligence officials believe Iraq's western Anbar province is the main entry point used by extremist groups, including Abu Musab al-Zarqawi's al-Qaida in Iraq, to smuggle in foreign fighters. Syria is under intense pressure from Washington and Baghdad to tighten control of its porous 612-kilometre border with Iraq.

On Thursday, a U.S. general called Syria's border the "worst problem'' in terms of stemming the flow of foreign fighters.

The next day, about 1,000 U.S. and Iraqi forces backed by tanks launched Operation Spear in the desert around Karabilah and Qaim. The offensive entered its second day Saturday in Karabilah, a dusty, blistering hot town about 320 kilometres west of Baghdad, is considered an insurgent hub.

About 50 insurgents have been killed since the operation began, U.S. marine Capt. Jeffrey Pool said from Ramadi, the provincial capital. Three U.S. troops have been wounded and about 100 insurgents have been captured, the military said.

Dozens of buildings in Karabilah were destroyed after air strikes and shelling.

"The goal is not to seize territory,'' said marine Col. Stephen Davis.

"This is about going in and finding the insurgents.''

Karabilah's streets were empty and the military said about 100 people fled the town. At one home, a family gathered on their porch, hanging a white flag from the roof to signal U.S. jets not to bomb their home.

Troops searching the town found four Iraqi hostages beaten, handcuffed and chained to a wall in a bunker, Davis said.

Some of the men were believed to be Iraqi border guards. Troops searching the bunker found nooses, electrical wire and a bathtub filled with water for electric shocks and mock drownings, Davis said.

Later, marines and Iraqi soldiers took fire outside a mosque and a small band of insurgents fled inside, Pool said. Three militants were killed.

The U.S. military also reported incidents of insurgents breaking into homes and using families as human shields, resulting in injuries to 10 civilians.

U.S. and Iraqi forces also found a bomb-making factory in the town, Pool said. It contained blasting caps, cellphones and other materials to make roadside and car bombs, he said. Troops also found sniper rifles, ammunition and a mortar system.

A nearby schoolhouse believed to be used for training had instructions for making roadside bombs written on a chalkboard, Davis said.

A second offensive of similar size, Operation Dagger, was launched Saturday, targeting the marshy shores of a lake north of Baghdad. About 1,000 marines and Iraqi troops, backed by fighter jets and tanks, took part.

Operation Dagger seeks insurgent training camps and weapons caches in the Lake Tharthar area, 85 kilometres northwest of Baghdad.

On March 23, U.S. and Iraqi forces killed about 85 militants at a suspected training camp along Lake Tharthar and discovered booby-trapped cars, suicide-bomber vests, weapons and training documents.

The insurgents captured then included Iraqis, Filipinos, Algerians, Moroccans, Afghans and Arabs from neighbouring countries, officials said.

The western region has been flush with militant fighters in recent weeks. Marines carried out June 11 air strikes that killed about 40 of them after a nearly five-hour gunfight on the outskirts of Karabilah.

Insurgents in the area also killed 21 people believed to be missing Iraqi soldiers. The bodies, including three that were beheaded, were found June 10.

Marines carried out two major operations near Qaim last month, killing 125 insurgents in Operation Matador and 14 in Operation New Market. Eleven marines were killed in those actions, which targeted insurgents using the road from Damascus, Syria, to Baghdad.

Iraqi troops did not participate in the earlier offensives. This time, they fought alongside the Americans and used their language skills and local knowledge to spot foreign fighters, said Col. Bob Chase, chief of operations for the Second Marine Division.

Separately, the U.S. military said Saturday two soldiers were killed and one was wounded after fighting with insurgents late Friday while transporting a detainee near Buhriz, about 55 kilometres north of Baghdad. A civilian and the detainee also were killed and five Iraqi police officers were wounded.

At least 1,718 members of the U.S. military have died since the Iraq war began in March 2003, by an Associated Press count.

In other violence Saturday, insurgents killed at least four people in Baghdad, including two Iraqi soldiers and a 10-year-old girl, hospital and police officials said. Twenty-one people -- including an Iraqi journalist -- were wounded in the suicide bombings and shootings. 

The girl was killed and two people were wounded when a roadside bomb missed a passing U.S. military convoy, said Dr. Muhand Jawad of Baghdad's Al-Yarmouk hospital.

A suicide car bomber slammed into an Iraqi army convoy in the Yarmouk neighbourhood, killing two soldiers and wounding six near dangerous road leading from downtown to the airport, police Lieut. Thaer Mahmoud said.

Also, a farmer found seven corpses in a field in eastern Baghdad, police said. The men, wearing civilian clothes, were shot in the back of the head and had their hands bound.

The body of a Sunni tribal leader also was found Saturday outside Mahmoudiya, about 30 kilometres south of Baghdad. Sheikh Arkan Shaalan Jassim al-Edwan, who had been shot, was sprawled on a fallen roadside portrait of deposed Iraqi president Saddam Hussein, police Lieut. Adnan Abdullah said.

More than 1,100 people have been killed since Prime Minister Ibrahim al-Jaafari's Shiite-led government was announced April 28.