Manila, Oct 4 : More than 3,000 Philippine and US troops started a series of joint military drills to sharpen their "interoperability in conducting combined tactical readiness". Acting Philippine Navy chief Rear Admiral Bernard Valencia said 630 Philippine troops, mainly from the marines, and 2,550 US marine soldiers are participating in the 12-day annual exercises, dubbed KAMANDAG 6. Japanese and South Korean troops are taking part as observers, he added. This year's exercise, running at various training sites in Metro Manila, throughout the main Luzon island and in Palawan province, will focus on "curbing transnational crime, counter-terrorism, and performing other non-traditional security roles," Valencia added at the opening ceremony. Rear Admiral Derek Trinque, Exercise Director on the US side, said coastal defence, amphibious operations and live-fire training will be included in this year's exercises, Xinhua news agency reported. /IANS