Two people were killed and at least four others wounded in a grenade attack blamed on Islamic militants in the southern Philippines, police and military said on Tuesday.
Men believed to be members of the Abu Sayyaf group tossed the grenade into a karaoke bar on Jolo island late on Monday, police said.
The Abu Sayyaf are also holding three Red Cross volunteers -- including an Italian and a Swiss national -- in Jolo's interior jungles and police said the attack could have been meant to divert military pressure on the kidnappers.
"The explosion targeted the beer joint," said Inspector Usman Pingay, the town's police chief.
"We have reports saying that the UTG was responsible for the attack," he said, referring to the Urban Terrorist Group, a unit of the Abu Sayyaf.
The blast came just hours after the Abu Sayyaf commander believed to be holding the hostages, Albader Parad, was reportedly wounded in a clash with troops.
Parad's men snatched the three hostages on January 15 while they were on a humanitarian mission to Jolo, an impoverished island and a stronghold of the Abu Sayyaf.
The group is blamed for the country's worst militant attacks, including the 2004 bombing of a passenger ferry that killed over 100 on Manila Bay.
It has kidnapped dozens of foreigners, businessmen and religious workers over the past decade and is on the US government's list of foreign terrorist organizations.