US forces played a "substantial" role in a botched raid against Muslim rebels in the Philippines that left 44 local police commandos dead, according to a Senate report released Tuesday.

The raid, known locally as Oplan Exodus, has plunged President Benigno Aquino's administration into crisis and jeopardized efforts to end a decades-long Muslim separatist insurgency.

"US personnel played a role in the training before, and monitoring, of the ... operation," Sen. Grace Poe told reporters as she released the findings of a committee inquiry into the January 25 raid.

"The committee found that the United States substantially invested in the entirety of Oplan Exodus. It provided equipment, training and intelligence."

Oplan Exodus sought to capture or kill two men on the US government's list of "most wanted terrorists" who were living among Muslim rebels in southern Philippine farming communities.

One of the men, Malaysian national Zulkifli bin Hir was reported killed.

But the other, Filipino Abdul Basit Usman, escaped as rebels surrounded the police commandos and killed 44 of them.

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A police inquiry earlier outlined a multitude of tactical errors that led to the slaughter of the commandos.

The Senate report said Aquino must "bear responsibility" for the deaths, but it also raised questions about the accountability of the United States, a longtime military ally of the Philippines that has so far declined to outline its role in the operation.

Three unnamed Americans were brought into the local army brigade headquarters during the operation, creating tensions at a crucial time with the Filipino military commander, according to the Senate report.

"One of the Americans ordered Maj. Gen. Edmundo Pangilinan to fire the artillery," the report stated.

"However Pangilinan refused and told him, 'Do not dictate to me what to do. I am the commander here.'"

A US embassy spokesman in Manila did not immediately respond to requests for comment about the Senate report.

The United States provides military training and intelligence to the Philippines in its counter-terrorism efforts.

Under the terms of an alliance between the allies, US forces are not allowed to engage in combat.

Poe said there was no evidence to show the United States was involved in combat, but said there were concerns that Washington's influence on the Philippine National Police (PNP) was too strong.