Philippine President Rodrigo Duterte has blamed the US CIA and his predecessor Benigno Aquino for a botched raid on a leader of an armed group that left 44 police dead.

"It was an American adventure with the cooperation of some, and apparently with your [Aquino's] blessing," Duterte said on the eve of the second anniversary of the Mindanao raid on Wednesday.

"Why was it kept under wraps? It was actually an operation of the CIA," he said during the event held at the presidential palace attended by widows and families of the slain officers.

READ MORE: Dozens of police commandos killed in Philippines

In January 2015, police commandos killed Zulkifli Abdhir, who was on the United States government's list of "most wanted terrorists", in a raid on a remote farmland area in the south, where various Muslim separatist rebel groups and other fighters are based.

Gunmen ambushed the attacking police commandos and killed 44 of them in a day-long battle. A Philippine Senate investigation blamed poor planning and coordination for the deaths.

The raid was carried out during the term of Duterte's predecessor Aquino, derailing efforts to make a peace pact with the main Muslim separatist group, the Moro Islamic Liberation Front (MILF).

Duterte's statement on Tuesday was the first time a Filipino official publicly linked the CIA to the incident.

During his seven months in office, Duterte has sought to loosen the Philippines' longtime alliance with the US, while forging closer ties with China and Russia.

'US forces on the scene'

Aquino had justified the police raid, saying that Zulkifli had been training armed fighters in the southern Philippines to make bombs.

The US had said Zulkifli was a top fighter of the Southeast Asian armed group Jemaah Islamiyah.

A Philippine Senate report into the raid later concluded the US played a "substantial" role by providing training, equipment and intelligence to the Filipino forces.

The Senate report did not refer to the CIA.

In a statement to Al Jazeera, Molly Koscina, spokesman of the US Embassy in Manila said, "We renew our heartfelt condolences to the family members of those who died trying to bring peace and stability to Mindanao.

"This operation was planned and executed by Philippine authorities. We refer you to them for details of the operation."

Jose Torres, a Filipino journalist who frequently covers the Mindanao conflict, told Al Jazeera that any CIA involvement remained unclear.

"What is clear, however, was US forces were on the scene of the incident. The US did not deny it. Some US military men were confirmed to be with their Filipino counterparts a few kilometres away," Torres said.

Torres also said unnamed sources privy to the operation said some "Caucasian-looking men" were among the casualties.

"Photos taken by journalists on the scene show US servicemen helping in the airlift of at least one soldier who appeared to be Caucasian," he said.

Richard Javad Heydarian, a Manila-based political analyst and professor, urge Duterte to form an "impartial, credible and balanced" investigative body to look into deaths.

"Command responsibility and the role of foreign powers is yet to be fully investigated," he told Al Jazeera. "The families need closure. The truth is yet to prevail."

With additional reporting by Ted Regencia.