MANILA (UPDATED) - US special forces are helping the Armed Forces of the Philippines (AFP) to end a siege of the southern town of Marawi City by militants allied to Islamic State, a US embassy spokesperson in Manila told Reuters.

Until now, there had been no confirmation that US forces were assisting in the battle for Marawi City, which is on its third week.

Their involvement comes after months of strain between the two allies stoked by Philippines President Rodrigo Duterte's hostility towards Washington and his pledges to throw out US troops who have long provided training and assistance.

"At the request of the government of the Philippines, US special operations forces are assisting the AFP with ongoing operations in Marawi that helps AFP commanders on the ground in their fight against Maute and ASG militants," the spokesperson said.

"For security reasons, we are not able to discuss specific technical details of US support for ongoing AFP operations," the spokesperson added.

In a press conference on Saturday afternoon, Philippine Army 1st Infantry Division spokesperson Lt. Col. Jo-Ar Herrera clarified that US forces were only providing technical support and are not part of clashes on the ground.

"They are not fighting. They are just providing technical support," Herrera said.

He said the US is helping in the exchange of intelligence reports and training.

"The presence of the US counterparts facilitate the exchanges of intelligence, facilitate subject matter experts exchange, and also provides training exchanges and, of course, the technical support that we are sharing together in the fight against global terrorism," he said.

On Friday, a US spy plane was seen flying over Marawi City.

The Philippine military earlier vowed to liberate Marawi City on Monday, Independence Day.

• Read: Military eyes Marawi liberation on Independence Day