Manila, Philippines ? Three explosions ripped through a major city Sunday in the southern Philippines, killing at least 14 people and injuring 45 others after a radio-station caller warned of a wave of bombings.

The caller claimed to be from the Muslim extremist group Abu Sayyaf, which has been holding an American missionary couple, Martin and Gracia Burnham of Wichita, Kan., for nearly 11 months and is the target of a U.S.-backed military campaign as part of Washington’s war on terrorism.

Police investigators gather evidence outside the Fitmart department store in General Santos, in the southern Philippines, following a bomb explosion that killed at least 14 people. Two other bombs exploded Sunday around the city. At least 45 people were injured in the blasts.

One bomb exploded outside a busy department store in downtown General Santos, killing at least 14 people four of them children in a hail of shrapnel and flying glass. Within 40 minutes, bombs went off near a radio station and a bus terminal in the largely Christian city of 800,000 in the Mindanao region, where Islamic militants have been fighting for an independent homeland.

The scene of blood, wreckage and shattered glass was reminiscent of five nearly simultaneous bombings in Manila 16 months ago that killed 22 people. An Indonesian man who has claimed he planned those blasts pleaded guilty Thursday in General Santos to explosives possession after leading police to a buried cache of more than a ton of TNT, detonating cords and M-16 rifles.

Police said it was too early to accuse any specific group of carrying out Sunday’s bombings, blaming only “terrorists.”

But a Radio Mindanao Network office in nearby Koronadal said it had received a call an hour before the first blast from a man who earlier called to complain about police boasts that the city was safe from terrorists. The man asked whether the station wanted to cover bombings later in the day.

A separate warning circulated via cell phone text message a chief method of communications in the Philippines said 18 bombs had been planted around the city and would start exploding after lunch.

Police said they had received an anonymous call with the same claim, but did not say what measures they had taken. Bomb threats are common in the Philippines.

Radio station manager Elmer Ubaldo said he had decided not to air the warning because he had not wanted to cause panic. The caller identified himself as Abu Muslim al-Ghazie and said he represented al Harakatul al-Islamiyah, the formal name used by Abu Sayyaf. Other spokesmen for the group said they had no knowledge of Abu Sayyaf involvement.

The Abu Sayyaf, believed to have ties to Osama bin Laden’s al-Qaida network, and the fundamentalist Moro Islamic Liberation Front have been blamed for setting off bombs in General Santos in the past.

The city is about 130 miles from Basilan island, where the Abu Sayyaf has been the Burnhams and Filipino nurse Ediborah Yap for nearly 11 months. About 160 U.S. Special Forces troops are on the island on a six-month counterterrorism training mission aimed at helping the Philippine military crush the guerrillas, who have beheaded an American and other hostages.

The first bomb exploded in a three-wheel motorcycle taxi parked in front of the two-story Gensan Fitmart department store in the business district of General Santos, about 620 miles southeast of Manila. Most of the casualties appeared to be taxi drivers, shoppers and bystanders.

The second went off 34 minutes later near a radio station, apparently causing no injuries, followed several minutes later by the bus terminal blast, which wounded several people, the city’s disaster operations center said.

Bartolome Baluyot, police chief for central Mindanao, said two unexploded bombs had been discovered under a truck parked in front of the store. Most businesses closed and checkpoints were set up on major roads as part of a security clampdown amid fears of further explosions.

The blasts came three days after the State Department renewed a warning urging Americans to exercise caution in the Philippines. In March, several bombs without triggering devices were discovered in Manila, and the rebel group that claimed responsibility has threatened to plant more bombs. The statement also noted that the Abu Sayyaf has kidnapped Americans and may do so again.