Abu Sayyaf rebels clashed with security troops in the southern Philippines on Saturday, 16 servicemen being killed and seven injured in the intense gunbattles, military sources informed.

According to a military spokesman, clashes broke out during the morning hours in the Ungkaya Pukan town in the Basilan province when security forces launched an offensive against Abu Sayyaf rebels that had a base in the region.

Thirteen marines died during the fire exchange, while two others deceased after suffering grave injuries. The pilot of a military helicopter was also killed after his aircraft plunged into the sea below for unknown reasons.

Rebels claimed that the chopper crashed after they opened fire on it, but the air force denied that enemy fire caused the crash, saying the aircraft stopped responding to commands and plummeted into the water. An investigation will be carried out, the co-pilot who survived the incident being able to scatter the mist surrounding the crash.

The rebels allegedly lost approximately 30 men and a regional commander. Ground troops were supported by air force planes and helicopters that bombed militants’ positions, opening the path for an assault carried out by marines.

The authorities deployed thousands of troopers in the region after 14 soldiers were killed last month near the town of Tipo-Tipo. Ten bodies were mutilated by rebels, an act that sparked the anger of authorities.

Moro Islamic Liberation Front (MILF) rebels claimed they have killed the marines during a firefight on July 10, but said no bodies were beheaded or mutilated as the army announced.

The rebels said they opened fire after a group of soldiers breached a previous deal made between the MILF and government by entering their territory without informing them. The Muslim separatist group has been engaged in peace talks with Manila officials, but the discussions ended last autumn due to several dissensions.

A similar operation was scheduled to be carried out against Abu Sayyaf rebels on the Jolo island, thousands of security troops being deployed there.