An improvised bomb has exploded at a bar in the Philippines' restive southern Mindanao region, wounding four people, police said on Sunday.
Witnesses saw a man acting suspiciously and leaving quickly before the bomb exploded at the Starlight Videoke bar in Tacurong city on Saturday evening, national police spokesman Chief Superintendent Agrimero Cruz said.
No group has claimed responsibility for the attack, although the Muslim separatist rebels and other armed gangs are known to operate in the area.
He said police and military had been put on alert to prevent similar attacks.
The explosion came just days after the US State Department warned of the risk of terrorist attacks in in parts of Mindanao, as well as in the capital Manila.
"Targeted sites may be public gathering places including, but not limited to, airports, shopping malls, conference centres, and other public venues," the advisory said.
The warning said that visitors should exercise "extreme caution" if travelling to Mindanao or the Sulu Archipelago.