Manila, May 21 : Philippine troops killed four more suspected rebels in a clash in the central Philippines on Sunday morning, a military spokesperson said. Lieutenant Colonel Israel Galorio of the Visayas Command said the clash between the troops and the News People's Army (NPA) insurgents broke out around 5 a.m. local time in Negros Oriental province, Xinhua news agency reported. Troops arrested a rebel while another surrendered after the 20-minute firefight, Galorio said, adding the troops also recovered firearms and ammunition. The clash in Negros Oriental brought to nine the number of NPA rebels killed during the weekend. On Saturday, troops killed five insurgents in the neighbouring Negros Occidental province. Galorio said no soldier was killed or wounded in the clashes. NPA rebels have been fighting the government since 1969. They concentrate their attacks on rural areas and have skirmishes with the military. Military data showed that the NPA is estimated to have 2,000 members, significantly lower than its peak strength in the 1980s. /IANS