U.S. personnel help their Philippine counterparts prepare to evacuate an injured police commando following clashes with Islamist rebels in January. (Mark Navales/AFP/Getty Images)

U.S. counterterrorism personnel played a hidden but key role in a bungled commando operation in the Philippines that resulted in dozens of deaths and a political scandal, according to a government investigation released Tuesday in Manila.

At least six Americans were present at a Philippine command post during the ill-fated January raid and supplied Philippine forces with surveillance data collected by U.S. aircraft, the investigation found. One of the Americans went so far as to order a Philippine army general to call in artillery fire, though the general angrily refused, investigators found.

The investigation by the Philippine Senate contradicts past statements from U.S. officials that Americans played no role in the operation except to help evacuate wounded Philippine police officers from a prolonged gun battle with Islamist rebels on the island of Mindanao. The raid targeted two terrorist suspects with multimillion-dollar U.S. bounties on their heads but ended in a deadly ambush, with 44 police officers and four civilians dead.

One of the targets of the raid, dubbed Operation Exodus, was Zulkifli bin Hir, a leader of a Southeast Asian militant network affiliated with al-Qaeda. A Malaysian citizen who received training as an engineer in the United States, he had been listed for years as a most-wanted terrorist by the State Department, which posted a $5 million reward for information leading to his capture.

Zulkifli was killed in the raid, according to Philippine officials. They said that they were forced to leave his corpse at the scene after the ambush but that they cut off his finger and sent it to the FBI to confirm his identity through DNA analysis.

The FBI has said laboratory tests indicated a DNA match based on biological samples collected from Zulkifli’s brother, who is serving time in a U.S. prison on terrorism charges.

Whom, exactly, the Americans involved in the operation were working for remains a mystery. The U.S. military has deployed several hundred Special Operations troops to the Philippines since 2002 as part of an anti-terrorism task force. But the Pentagon was cagey about whether any of its troops were involved in the Mindanao raid.

Marine Lt. Col. Jeffrey Pool, a Pentagon spokesman, said the operation “was planned and executed by Philippine authorities.” In an e-mail, he confirmed that American “contract personnel” assigned to the anti-terrorism task force had helped evacuate Philippine casualties after the firefight. When asked whether U.S. military forces played a role, he referred questions to the U.S. Embassy in Manila and the State Department.

The State Department, in turn, declined to answer questions about the incident. In a statement, Jen Psaki, a State Department spokeswoman, said the operation “was planned and carried out by Philippine authorities” and referred queries to them.

Although the U.S. anti-terrorism task force in the Philippines is composed primarily of Special Operations forces, it is common for the elite troops to work with intelligence operatives from the CIA and other agencies. A CIA spokesman also referred questions to the State Department.

The Philippine Senate report did not specify whether the six Americans were wearing uniforms or which agency they worked for. The report identified one as “Mr. Al Katz” and said he was responsible for training a Philippine police commando unit known as the Seaborne. The other Americans were not named or described.

A separate investigative report released Friday by the Philippine National Police also asserted that six Americans were present at a command post during the operation and that some of them helped evacuate the wounded Philippine commandos by helicopter after the ambush.

The national police report stated that the U.S. personnel played a crucial role by providing “real-time information on the actual movements of friendly and enemy forces” that was collected by U.S. surveillance aircraft hovering overhead.

The detailed accounts of U.S. involvement raise questions of whether the Americans were partly culpable for the operation, which has triggered a national political scandal in the Philippines and the downfall of high-ranking security officials.

The investigative report by the national police, however, credited the Americans with helping to avert an even greater disaster. It found that the U.S. surveillance data enabled one Philippine commando unit “to elude large enemy formations, thereby avoiding further casualties.”

Under Philippine law and the terms of a defense treaty with Manila, U.S. military forces in the country are prohibited from engaging in combat, except in self-defense. In practice, however, they have long played a supporting role in counterterrorism operations by serving as advisers and collecting intelligence.

Another terrorist suspect on the U.S. most-wanted list is believed to have narrowly escaped Philippine forces. Abdul Basit Usman, a Filipino citizen and accused bombmaking expert, has a $1 million U.S. bounty on his head.

Zulkifli and Usman were hiding in territory controlled by the Moro Islamic Liberation Front, which has been waging an insurgency against the government of the Philippines for decades. The rebels had signed a cease-fire with the government last year, an accord that was placed in jeopardy by the raid.

Greg Miller contributed to this report