It was not immediately known how many people were killed in the raid on the convoy early Thursday local time, but officials said there was no indication that any senior Iraqi leaders were among them.

Five Syrian nationals were injured in the course of the operation, three of whom were treated for their injuries, said a defense official, who spoke on condition of anonymity. Another official said the Syrians were border guards wounded in a subsequent firefight.

It was unclear whether the fighting spilled over into Syrian territory, officials said.

The clash came after US forces attacked a convoy of six or seven vehicles, striking some in a compound in western Iraq near the Syrian border and others as they moved away from it, a defense official said.

US special forces and airborne troops backed by multiple aircraft, including an AC-130 gunship and helicopters, took part in the attack which was launched in response to intelligence that the convoy was carrying people associated with the deposed Iraqi regime, officials said.

It was unclear how US forces came into contact with Syrian border guards, an official said.

"It could have been special forces, it could have been airborne forces. The reporting is unclear," said the officials, who spoke on condition of anonymity.

"There were a few Syrian nationals involved in the incident," said Lieutenant Colonel Gary Keck, a Pentagon spokesman. "A few may have been injured. We are treating those."

"It is still to be determined which side of the border" the convoy was on when it was hit, Keck said, adding that the United States was working with the Syrian government.

Another defense official said 20 people were captured in the attack, but most of them were released after it was determined they were not a threat.

The attack has prompted reports that US officials believed deposed Iraqi leader Saddam Hussein or his sons may have been in the convoy.

But a US defense official with knowledge of the intelligence that led to the strike, said reports that Saddam or his sons were hit were "wishful thinking."

"We don't have specific details yet who was in the convoy or the number of enemy forces," another defense official said.

"We do not have any confirmation of the identity of any individuals who might have been killed. Site exploitation continues, and routine DNA testing will be done if appropriate based on all intelligence gathering," the official said.

The White House would not say if Saddam or his sons were believed to have been in the convoy.

"I can confirm for you that there were military operations against leadership target or targets," White House spokesman Ari Fleischer told reporters.

"This should be seen in keeping with the ongoing military effort in Iraq to bring justice to people who we believe are associated with the regime or are leaders in the regime," added the spokesman.

US defense officials, who spoke on condition of anonymity, said they knew of no effort to collect DNA samples at the site.

Hopes of capturing the ousted Iraqi leader have risen since the detention one week ago of Saddam's closest aide, Abid Hamid Mahmud in northern Iraq.

Mahmud, number four on the US list of 55 most wanted Iraqis, has told his US captors that Saddam and his sons survived the war, the official confirmed.

Mahmud said he fled with them to Syria, but they were expelled following US pressure.

"That's what he said," said the official. "We don't know if it's true."

Saddam and his sons were the targets of at least two US air strikes during the war, but their fate is unknown.

The failure to account for them has given Iraq's former Baathists ruling party a rallying cry to resist the US occupation, US commanders and administration officials believe.

Near daily hit-and-run attacks have claimed mounting US casualties, prompting intensive US raids to crush the resistance before it can take root.

WAR.WIRE