United States special forces are providing support to the Philippine military battling to dislodge Islamist militants in a southern city, the US embassy said Saturday, as 13 Filipino marines were killed in fresh fighting. Philippine troops are struggling to defeat hundreds of fighters, who rampaged through Marawi on May 23 flying black flags of the Islamic State group, and have used bomb-proof tunnels, anti-tank weapons and civilians as human shields to fortify their positions.