MANILA, Philippines >> Suspected Islamic militants detonated a powerful bomb that killed at least three people and wounded 27 others in a budget hotel packed with wedding guests in the southern Philippines, officials said Monday.

Investigators believe the blast and ensuing fire that gutted the two-story Atilano Pension House in downtown Zamboanga City late Sunday was a terrorist strike and that it was not linked to the wedding, city police director Edwin de Ocampo said.

Still, many of the victims were from a group of more than 20 people who occupied six of the hotel’s 35 rooms for a planned ceremony Monday. The tragedy forced the wedding to be postponed, Zamboanga Mayor Celso Lobregat said.

“We should not show that we’re panicking because that is what these troublemakers relish to see,” Lobregat told The Associated Press by telephone. “We have good leads. We will get all of them.”

The blast was believed to be one of two simultaneous bombings planned by al-Qaida-linked Abu Sayyaff militants. The other would have been on nearby Basilan island, where two explosives were separately found and safely defused by authorities in Isabela city on Sunday, de Ocampo said.

The hotel blast, caused by about 22 pounds (10 kilograms) of TNT powder, was one of the most high-profile bombings this year blamed on the Abu Sayyaf, which has been weakened by years of battle setbacks.

The blast was so powerful it caused much of the second floor to collapse, blew off the hotel roof and shattered glass panes and windows from nearby buildings, Zamboanga city Mayor Celso Lobregat said.

Two of the wounded were in serious condition and more than a dozen others remained confined in a hospital, he said.

Zamboanga city, a predominantly Christian trading hub 540 miles (860 kilometers) south of Manila, is located in a volatile region long troubled by a decades-long Muslim insurgency, extortion gangs and kidnap for ransom syndicates.

The blast occurred in room 226 on the second floor of the hotel, instantly killing two people staying in two adjacent rooms, which were devastated by the blast. A third body was found Monday on the ground floor, pinned by the cement slabs that collapsed from above, Lobregat said.

De Ocampo said investigators were trying to determine how the TNT bomb was detonated, adding its design resembled those used by the Abu Sayyaf in past attacks on Basilan island, the group’s birthplace.

Police Senior Inspector Cesar Memoracion said his local bomb squad recently informed the hotel owner to be on guard for a possible bomb attack, citing intelligence, which did not identify the source of the threat.

In January 2000, the hotel was rocked by a blast that killed three suspected Muslim militants assembling a bomb in a room, officials said.

The Abu Sayyaf was founded on Basilan in the early 1990s as an offshoot of a violent Muslim insurgency that has been raging for decades. U.S.-backed offensives have weakened the group, which is blacklisted by Washington as a terrorist organization, but it remains a key security threat.

It has about 380 armed fighters and survives mostly on extortion and kidnappings for ransom. Abu Sayyaf militants are believed to be holding an American, an Indian, a Malaysian and a Japanese convert to Islam, along with a number of Filipino hostages in Basilan and nearby Jolo island.