Davao City, Philippines - Philippine President Rodrigo Duterte has warned that more blasts could hit the country because of "reprisals" against his government, a week after a bombing killed 14 people and injured more than 60 others in his home city.
Arriving in Davao after his first foreign trip as president, Duterte told reporters on Saturday that it was too early to talk publicly about any leads being pursued by those investigating the September 2 attack.
"But I guarantee you that there will be a day of reckoning. So watch out," Duterte said in a mix of English and Filipino.
Duterte was returning on Saturday from a visit to Indonesia, which followed his trip to Laos to attend the Association of Southeast Asian Nation (ASEAN) summit.
Duterte did not mention a specific group involved in the attack. But after the blast, he ordered the army to carry out a major operation in the Sulu province, sending at least 7,000 troops to a province long known as a stronghold of the Abu Sayyaf armed group.
Senior government officials had earlier blamed Abu Sayyaf, an armed group that has pledged loyalty to the Islamic State of Iraq and the Levant (ISIL, also known as ISIS), for the Davao blast.
The Philippine navy had imposed a blockade to stop fighters from slipping out of the notoriously porous southern border next to Malaysia and Indonesia.
An ongoing military offensive has killed at least 32 fighters and left more than a dozen government soldiers dead.
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In Davao, Sara Duterte, city mayor and daughter of the president, has raised a reward offered for those behind the attack from $20,000 to $30,000, a hefty amount in the Philippines.
On Saturday afternoon, state broadcaster PTV reported that a politician from Mindanao had been arrested after being linked to the attack. He was identified as Talitay, Maguindanao vice mayor Abdulwahab Sabal. He has denied the allegations, according to the ABS-CBN website.
Sabal and his brother, Montasir Sabal, Talitay mayor, have also been linked to the illegal drug trade in their province, the PTV report said.
On Friday in Indonesia, Duterte told a group of Filipino workers that he wanted Abu Sayyaf "blown up" at sea.
He said that Indonesia "can go ahead and blast them [Abu Sayyaf] off" in the event of a chase in the high seas between the two neighbouring countries.
Duterte said the Indonesian navy had the right to enter Philippine territory if they were pursuing the armed group, adding that the Philippine navy would work closely with it "to end this problem once and for all".
After a meeting with President Joko Widodo, Duterte issued a statement saying: "We expressed commitment to take all necessary measures to ensure security in the Sulu Sea and maritime areas of common concern."
In May, the Philippines, Indonesia and Malaysia reached an agreement to coordinate patrols in shared sea routes.
Abu Sayyaf, whose name translates as "Bearer of the Sword", has been involved in a spate of kidnapping cases in Muslim-majority Sulu and elsewhere in the southern Philippines for years.
It is believed that it is currently holding at least nine Indonesians and seven other foreign nationals.
In June and April, the group claimed responsibility for the beheadings of two Canadians.
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Abu Sayyaf emerged in the early 1990s during a separatist rebellion being fought by minority Moro Muslims in the south of the predominantly Roman Catholic Philippines.
Conducting bombings, kidnappings, beheadings and extortion, the group's kidnap-for-ransom operations have become a lucrative business for the group.
In 2017, the Philippines will host the annual ASEAN summit.
Asked if Davao could be the venue, Duterte said it would depend on the security situation.
"I would have to listen to the military and the police for an accurate assessment," he said.