A bomb explosion rocked a southern Philippine public market on Wednesday, killing at least six people and wounding 22 others, officials said, amid warnings that Muslim militants may try to disrupt this weekend's Asian regional summit.

The blast ripped apart a lottery outlet across the public market in General Santos city, 620 miles southeast of Manila, said Senior Superintendent Alfredo Toroctocon, the city police chief.

He said three people died instantly and another two succumbed to wounds. Staff at the St. Elizabeth Hospital in the city reported another person died on arrival, bringing the death toll to six.

Chief Superintendent German Doria, the regional police chief, said police had no suspects immediately but that the regional militant network Jemaah Islamiyah and its ally, the local Abu Sayyaf group, "usually are the ones doing all these explosions in the region."

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But he said police also were looking into the possibility that the blast stemmed from the failure of the lottery outlet operator to pay winners of a lottery draw.

"This Lotto outlet closed three days ago because many bettors won ... then all of a sudden an explosion occurred in front of the Lotto outlet," Doria said.

Philippine National Police chief Oscar Calderon, who is in Cebu to oversee security for the summit, said earlier Wednesday that militants may try to embarrass the government, a staunch U.S. ally in counterterrorism, by staging attacks during the summit.

Chief Superintendent Romeo Ricardo, director of the national police Intelligence Group, said police and army troops have launched operations against militants throughout the archipelago to prevent them from carrying out attacks.

Those operations led to the killing of five members of the local Abu Sayyaf Islamic extremist group and an Indonesian militant in southern Tawi Tawi province last week, and the arrest of a bomb suspect two days earlier just southeast of Manila, he said.

On Wednesday, military Chief of Staff Gen. Hermogenes Esperon said troops killed another senior Abu Sayyaf member, Binang Sali.

Terrorism is a concern at the summit of the 10-member Association of Southeast Asian Nations and their partners from Australia, China, Japan, South Korea, New Zealand and India. Most foreign and economic ministers arrived Wednesday ahead of their leaders.

Australia said Monday it had received information suggesting terrorists were "in the final stages of planning attacks" on a range of targets in the Philippines, particularly in the southern Philippines, where Muslim insurgents and Al Qaeda-linked militants are active.

But Philippine officials insisted security for the summit was tight, with police and troops on the highest alert.

The Philippines last month postponed the summit, originally set for Dec. 11-13, at the last minute, citing an approaching typhoon. But some delegates suspected concerns over a terror attack were the real reason.

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