COTABATO, Philippines : An escalation of fighting between the Philippine army and a breakaway Muslim rebel group in the country's south killed 18 people in a single day of violence, the military said Tuesday. Seventeen members of the rebel Bangsamoro Islamic Freedom Fighters (BIFF) and one soldier were slain in the day-long violence Monday in the strife-torn southern island of Mindanao, Brigadier General Eduardo Pangilinan, the area's military commander, said."One of our soldiers was killed during the (initial) attack. The 17 enemies were killed when our troops fired back and during the subsequent encounters," the general told reporters. There was a lull in fighting on Tuesday but the military remained on alert, with helicopter gunships flying overhead and armoured vehicles parked on the streets of Cotabato City, a trading centre in the area."There have been no additional encounters but we are continuing our operations on the ground," Pangilinan added.Fighting began in the early hours of Monday morning as BIFF guerrillas attacked military outposts in the violence-scarred province of Maguindanao.The violence later spread to the neighbouring province of North Cotabato before the rebels pulled back, Pangilinan said.BIFF spokesman Abu Misry Mama disputed the military's version of events, saying only four of his fighters had been killed."Only four have died. We would never lie about our casualties because it is an honour to die as a mujahedeen," he said.He said the BIFF had launched the attacks in retaliation for the military's abduction of a Muslim father and son on July 3.The military has previously denied his accusation, branding this as propaganda.Regional social welfare agencies said that at least nine civilians were wounded and over 300 families had been forced to flee due to the new fighting.The BIFF split from the main Muslim rebel group, the Moro Islamic Liberation Front (MILF), in 2008.The 10,000-strong MILF has entered into a ceasefire and peace talks with the government for the creation of an autonomous region for Muslim-dominated areas in the south of this largely Christian nation.However the BIFF, which is believed to have just a few hundred fighters, has rejected the negotiations and still demands a separate Islamic state in the southern Philippines.It has previously launched attacks in Mindanao in efforts to disrupt the peace efforts.Various Muslim armed groups including the MILF have waged a rebellion in the southern Philippines since the 1970s aimed at winning independence or autonomy for the country's Muslim minority in Mindanao, which they regard as their ancestral homeland.About 150,000 people are estimated to have died in the conflict.