MANILA, Philippines -- Two bombs exploded Tuesday in insurgency-torn southern Philippines, killing six people and wounding more than 30, as officials heightened security amid warnings al-Qaida-linked terrorists were planning further attacks.

One explosion occurred in a stall selling alcohol during a festival in the town Makilala on Mindanao island, said North Cotabato provincial Police Chief Federico Dulay. Six people were killed and at least 29 injured.

The second bomb went off in a market in Tacurong on another part of the island, wounding five people. A security guard spotted the bomb hidden in a bag and threw it away from the crowd before it exploded, army Col. Felipe Tabas said.

The U.S., Australian and British embassies issued warnings against travel to Mindanao and said the threat of imminent attacks or kidnappings is high across the archipelago, specifically in places frequented by foreigners.

“We believe that terrorists are in the final stages of planning further attacks,” said the British advisory, posted on the embassy’s website.

“There is a high threat from terrorism throughout the Philippines.”

The embassies cited “credible” intelligence, with the Australian website saying: “These reports indicate that attacks are imminent and could occur at any time.”

Philippine officials said the attacks could be in retaliation for the arrest of a fugitive terror suspect’s wife last week.

Istiada Binti Oemar Sovie was arrested on Jolo island, in the Mindanao region. She is the wife of Dulmatin, one of Asia’s most wanted terror suspects, who has been linked to the 2002 Bali bombings that killed 202 people.

He and another Indonesian, Umar Patek, are believed to be hiding on Jolo with guerrillas belonging to the Abu Sayyaf terror group, which has ties to al-Qaida. Washington has offered a US$10-million reward for the capture of Dulmatin and $1 million for Umar Patek.

Bombs such as the ones that exploded Tuesday have been used in the past by Abu Sayyaf but investigators were trying to determine if other groups, like extortion gangs, were involved, said police Chief Supt. German Doria.

Washington has deployed troops to Mindanao since 2002 to arm and provide training to Filipino troops battling the militants. U.S. troops also have provided assistance to track down Indonesian and Filipino militants on Jolo.

The Associated Press