Quezon City, Philippines ? A bomb tore through a passenger bus Friday night in a Manila suburb, killing at least three people and injuring 23 the latest in a series of bombings this month in a jittery country where U.S.-trained troops are battling a Muslim rebel group linked to al-Qaida.

There were no immediate suspects or claims of responsibility, police said. The passenger who brought the explosive aboard the bus was believed to be among the dead, but it was unclear whether the blast was intended as a suicide attack.

“I was sleeping, then there was a very loud explosion,” teenage student Merlyn Villareal, who was aboard the bus but was not injured, told GMA7 television as she fought back tears. “There was chaos, and I was pinned down. I was kicked around and found myself outside the bus.”

The explosion in Quezon City came a day after two deadly bombings in the southern Philippines, and hours after a grenade blast in the capital’s financial district.

Officials said the Abu Sayyaf, which the Philippine and U.S. governments have linked to al-Qaida, was the most likely suspect for Thursday’s bombings in Zamboanga city, which killed seven people and injured more than 150.

The Abu Sayyaf recently threatened attacks in retaliation for an ongoing military offensive against it, and it has been blamed for an Oct. 2 bombing in Zamboanga that killed four people, including an American Green Beret.

Some 260 American troops remain in Zamboanga in the southern Philippines following a six-month U.S. counterterrorism training exercise aimed at helping Filipino troops fight the Abu Sayyaf.

Earlier Friday, President Gloria Macapagal Arroyo visited the Zamboanga bombing sites, saying the country’s bomb attacks have gone from “bad to worst” and urged her people to help fight terrorists.

“Terrorism cannot survive for long in an unfriendly environment,” Arroyo said. “Let us give terrorism the unfriendly environment.”