Gathering intelligence has proven difficult in a complex society of religious, ethnic and tribal rivalries, where government records were burned or stolen in the looting that followed the collapse of Saddam Hussein's regime in April.

There have been few claims of responsibility for any attacks except for a couple of grainy videotapes. The best clues have come from interrogating suspects - difficult to authenticate - or from forensic evidence, such as that which pointed to the use of powerful plastic explosives in vehicle-bombings this week in Baghdad.

A senior U.S. counterterrorism official said Thursday that use of those explosives, which the official said were traced to a manufacturer outside Iraq, pointed to possible al-Qaida involvement.

U.S. forces have seized large caches of plastic explosives among the munitions believed left over from Saddam's rule, indicating that they could have come from undetected Iraqi supplies.

On Thursday, U.S. Undersecretary of State John Bolton told the British Broadcasting Corp., that U.S. commanders believe "elements of the previous...regime" have linked up with "international terrorists" to strike at U.S. and coalition forces.

Bolton added the attacks "demonstrated to many Iraqis that they are being used by al-Qaida and other terrorist groups ..."

References to attacks in Baghdad and the name al-Qaida suggest a link with Osama bin Laden's terror network. That link resonates among Americans scarred by the Sept. 11, 2001, attacks but increasingly skeptical of the U.S. role in Iraq.

However, senior American officers in Iraq have carefully avoided focusing on al-Qaida. They believe some foreign fighters may be involved in the insurgency, along with Saddam loyalists. But the number of foreign fighters remains a mystery.

"We believe there is in fact a foreign fighter element," Lt. Gen. Ricardo Sanchez, commander of U.S. forces, told reporters Oct. 2. "There is a terrorist element focused on the coalition and international community in general and the Iraqi people to try to disrupt the progress being made."

However, Sanchez told reporters on Oct. 22 - three days before the missile attack on the Al-Rasheed Hotel - that "we don't have any confirmed al-Qaida operatives in custody at this point."

The New York Times, citing unidentified senior officials, also reported on its Web site Thursday night that U.S. officials believe Saddam himself may be playing a significant role in coordinating and directing attacks by his loyalists.

Some commanders have openly expressed skepticism about any influx of foreign fighters.

Brig. Gen. Martin Dempsey, the commander of the 1st Armored Division that controls Baghdad, told reporters Sunday that "we have not seen any infusion of foreign fighters."

"We haven't seen them yet," Maj. Gen. Maj Gen. Ray Odierno, commander of the 4th Infantry Division based in Tikrit, said of foreign fighters. "We continue to look for that every day."

Before the war, Saddam and his top lieutenants claimed they were recruiting foreigners to fight the Americans and even arranged a visit by reporters to a training camp near Baghdad in March.

Most of the recruits at the camp wore beards, chanted slogans glorifying holy war, voiced deep hatred for America and said they would seek martyrdom on the battlefield.

The volunteers said they came from Algeria, Libya, Tunisia, Egypt, Syria and Saudi Arabia. Journalists and Iraqi civilians spoke of seeing non-Iraqi Arabs fighting alongside Fedayeen troops in Baghdad, but many of them were believed to have fled Iraq after the regime collapsed.

In Washington, a senior defense official told reporters Wednesday that a link had been found between Saddam supporters and foreign fighters.

The official said on condition of anonymity that two members of the Islamic extremist group Ansar al-Islam told interrogators that Izzat Ibrahim al-Douri, No. 6 on the list of 55 most wanted Iraqis, was coordinating attacks with foreigners.

The official described the report as the first solid indication that foreign fighters and Saddam loyalists are working together to fight Americans here.

However, the link between Ansar al-Islam and foreigners is not altogether clear. Most members of Ansar al-Islam are believed to be Iraqi Kurds, some of whom may have trained in Afghanistan with al-Qaida.

U.S. officials have alleged that Ansar al-Islam offered safe haven to Abu Musaab al-Zarqawi, a Jordanian sought in the assassination of a U.S. diplomat in Jordan. A key Ansar figure, Aso Hawleri, also known as Asad Muhammad Hasan, reportedly was captured in the northern Iraqi city of Mosul this month.

In the weeks leading to the war, Ansar al-Islam wasn't even on the U.S. list of terrorist organizations. Much of the information on the organization appears to have come from rival Kurdish groups with close ties to the United States.

Ansar al-Islam, or "Helpers of Islam," was formed in northern Iraq in 2000 and stepped up its activities the following year.

Ansar's leader since 2001, Najm al-Din Faraj Ahmad, is an itinerant religious teacher better known as Mullah Krekar. He lives in Norway, where he has held refugee status since 1991.

Krekar, who opposed Saddam and has denied links with bin Laden, says his U.S.-backed rivals in Kurdish-dominated northern Iraq have tried to link him to Saddam and bin Laden to discredit him.

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