Hambali (search), alleged mastermind of Al Qaeda's campaign of bombings in Southeast Asia, was plotting new terror attacks when he was captured this week, possibly against a Bangkok summit President Bush is due to attend, Thailand's prime minister said Saturday.

Hambali, an Indonesian whose real name is Riduan Isamuddin, planned to make Thailand a base for terror operations, but his arrest -- and those of three of his associates since June -- has uprooted his Jemaah Islamiyah (searchterror network from the country, the Thai leader said.

Thailand's porous jungle and river frontiers and lax security at border posts make it a tempting place for Jemaah militants to hide. But its cells have been more prominent in other nations of the region -- Malaysia and Indonesia. Indonesia -- scene of the group's deadliest bombings -- increased security during Independence Day celebrations this weekend, fearing revenge attacks.

But a top U.S. official said it would be a "foolish assumption" to believe the threat of terrorist attack at the Asia-Pacific Economic Cooperation (searchforum in October ended with Hambali's arrest.

"We have a top planner, we do not have all the members of Al Qaeda in our possession, or Jemaah Islamiyah in this case," U.S. Deputy Secretary of State Richard Armitage said during an interview broadcast Sunday on Australian television.

"I think a better assumption is that these fellows are out to do us ill and we ought to take every precaution against this."

APEC, set for Oct. 20-21 in the Thai capital, is expected to attract at least 20 world leaders, including Bush.

"The result of investigations show that Hambali came to Thailand not only to seek a safe haven but he also planned to make a move during the APEC meeting," Prime Minister Thaksin Shinawatra (searchtold reporters. He refused to elaborate.

"He came here to work and was using Thailand as a base for committing acts of terror. Investigations reveal some connection to APEC, but we still have to investigate further," Thaksin said.

The 39-year-old Islamic cleric was captured by CIA agents and Thai forces in a raid Monday on his apartment in the ancient temple city of Ayutthaya, 50 miles north of Bangkok. Thai military sources say he was handed over to U.S. investigators and flown out of the country on Wednesday, and Thaksin would not comment on his whereabouts.

U.S. investigators will seek to determine if Hambali had any success with the assignment a Bush administration official said was given soon after the Sept. 11 terror attacks in the United States: recruiting new hijackers.

On Saturday, President Bush thanked Thailand's prime minister for his country's help in capturing Hambali, and promised Indonesia's leader that information from the man's interrogation would be shared.

Bush phoned Thaksin to "express our appreciation for the role the Thais played in the capture of Hambali," White House spokesman Scott McClellan said.

Hambali, said to have trained under Usama bin Laden in Afghanistan in the 1990s, is reported to have been close to Khalid Shaikh Mohammed, the alleged Sept. 11 organizer captured earlier this year, and is believed to have hosted a meeting of senior Al Qaeda operatives, including two Sept. 11 hijackers, in Kuala Lumpur in January 2000.

But in Southeast Asia, he is seen foremost as the militant who brought Al Qaeda-style attacks to several countries in the region, including the October bombings in Bali, Indonesia, that killed 202 people, mostly foreign tourists.

Thaksin said the arrests of three Hambali associates in recent months led to Asia's most wanted man. Among those caught by Thailand was Zubair Mohamad, a Malaysian believed to have been instrumental in Jemaah Islamiyah's financial dealings, Thai and Malaysian newspapers reported Saturday.

The trail began exposed by an "irregular money transaction" noticed by investigators, the Thai premier said in his weekly radio address to the nation.

This "resulted in the arrest of the first case, the second, the third, and now we have got the fourth man -- Mr. Hambali -- who is regarded as the last one in our land," he said.

"Finally we have got them all," he said.

In Indonesia, soldiers and police tightened security at high-risk targets -- including hotels, malls, bars and offices of foreign companies and churches -- for the country's Independence Day celebrations on Sunday amid fears of more terrorist attacks.

"The government will do everything within its powers to secure and guarantee security during the celebrations in Indonesia," Security Minister Susilo Bambang Yudhoyono said after a security meeting at the presidential palace.

Thai authorities also have handed over Hambali's wife to Malaysian police, who believe she has crucial information about her husband's activities, a Malaysian newspaper reported.

Noralwizah Lee Abdullah, a 33-year-old Malaysian citizen, was arrested Monday night with her husband in Ayutthaya and has since been flown to Malaysia under police escort and brought to a secret location for questioning, The Star newspaper said, citing unidentified sources.

Malaysian police said they could not confirm the report.

Jemaah Islamiyah is also blamed for the Jakarta Marriott Hotel bombing (searchon Aug. 5 that killed 12 people, as well as attacks on churches in the Philippines and foiled plots to attack diplomatic missions in Singapore.

Indonesia's national police chief, Gen. Da'i Bachtiar, said Sunday that nine people have been arrested in connection with the hotel bombing, but he gave no details.

He also said the Indonesian national police would dispatch two of its interrogators to question Hambali, as soon as U.S. approval is received.

Indonesia has said it would demand access to Hambali and his eventual extradition to stand trial here.

President Megawati Sukarnoputri telephoned President Bush on Saturday to discuss the matter, Foreign Minister Hassan Wirayuda said after a national day ceremony Sunday at the presidential palace.

Thai authorities are believed to have known Hambali was in the kingdom in January last year, when he planned the Bali bombings at a meeting in Bangkok. He is believed to have returned to Thailand more recently, using a fake Spanish passport to enter from neighboring Laos, local newspapers reported.