MANILA (REUTERS) - Philippine President Rodrigo Duterte said on Sunday (June 11) he was not aware of US support to end the militant siege in the southern city of Marawi, and had "never approached America" for help.

"I am not aware of that until they arrived," Duterte told a media briefing when asked about US support to fight the Muslim militants in Marawi City.

Duterte was speaking a day after Philippine military officials said US special forces was providing technical assistance to end the siege of Marawi by fighters allied to Islamic State in Iraq and Syria (ISIS), which is now in its third week, but it had no boots on the ground.

"They are not fighting. They are just providing technical support," military spokesman Lieutenant Colonel Jo-Ar Herrera told a news conference in Marawi City.

The Pentagon, which has no permanent presence in the Philippines but for years has kept 50 to 100 special forces troops in the south of the country on rotational exercises, confirmed it was helping the Philippine military in Marawi.

It said in a statement it was providing Philippine forces with security assistance and training in the areas of intelligence, surveillance and reconnaissance. It said it had an additional 300 to 500 troops in the country to support regular training and activities, without giving further details.

Speaking on condition of anonymity, a US official said support included aerial surveillance and targeting, electronic eavesdropping, communications assistance and training.

A US P-3 Orion surveillance plane was seen flying over the town on Friday, according to media reports.

This story is developing.