The foreign troops were deployed in non-combat, support roles, a Philippine commander said. Manila faces claims that it was warned about the militants before they seized areas of central Marawi.
Almost 300 militants, soldiers and civilians have died in a siege that has underscored the rise of militancy in Southeast Asia and undermined central planks of President Rodrigo Duterte’s claims to be tough on national security while bringing peace to the large, predominantly Muslim southern island of Mindanao.
A few hundred civilians are believed to be either trapped by fighting or being held hostage by Islamists led by Isnilon Hapilon, an Abu Sayyaf commander.
Hapilon, the leader of the so-called Islamic State in Southeast Asia, is on the FBI most-wanted list of terrorists, with a US$5 million bounty.
Military spokesman Brigadier General Restituto Padilla said the US forces at Marawi but were not allowed to fight. “There are some US personnel who are operating equipment to provide information on situation awareness to our troops,” the officer said.
He added that the US and Philippines signed a mutual defence treaty in 1951 that called for them to aid each other if attacked by a third party.
The US said the assistance was part of a long-term counterterrorism strategy, noting that special forces were “providing support and assistance in the southern Philippines for many years”.
Duterte has expressed hostility towards the former colonial master, demanded troops were expelled from the archipelago and said the Washington treated the Philippines “like a dog tied to a post”. The 72-year-old Duterte has also said that he did not seek US help for the Marawi operation.
His hostility to the US was partly fuelled by his student years during the Vietnam War, when he was educated by left-wing academics.
The Philippine constitution prohibits the presence of foreign combat troops.
The Philippine government said there was intelligence in early May that the Isis-linked group planned to occupy Marawi.
Duterte imposed martial law on his native Mindanao with the possibility it could be extended nationwide.
Philippine and US troops on exercise together in 2013. Picture credit: US Marines