BALI, Indonesia — Investigators hunted yesterday for the two suspected masterminds of suicide bombings on this resort island as Indonesia, Thailand, the Philippines, Australia and other nations went on high alert to protect their beaches from a repeat of the weekend attacks.

Newspapers published photographs of the three alleged bombers' severed heads, evidence that investigators hope will lead them to the two Malaysians believed to have plotted Saturday's attacks at crowded restaurants that killed at least 22 people besides the bombers and wounded 104, including six Americans.

"It is our hope that people will recognize the faces and call us," police Brig. Gen. Sunarko Dami Artanto said as he released two hot-line numbers. "It will help us speed up the investigation."

The men suspected of masterminding the attacks — Azahari bin Husin and Noordin Mohamed Top — allegedly are key figures in Jemaah Islamiyah, a regional Islamic militant group with links to al-Qaida that is blamed for the 2002 Bali nightclub bombings that killed 202 people, mostly foreigners.

Azahari is known as "Demolition Man" for his knowledge of explosives, while Noordin has been dubbed "Moneyman" for his ability to raise money and recruit bombers.

Police also sought three accomplices believed to be still on the island.

Police said today that two men had been detained for questioning, though neither was officially named a suspect. Police also have questioned 39 witnesses about the bombings, said police spokesman Sunarko.

The bombings came as Southeast Asia geared up for its major tourist season, when millions of Europeans and other foreigners flock to sunny beaches. It was the second attack targeting Bali in three years.

Indonesia's security level was raised to "top alert" after Saturday's attacks, with two-thirds of the vast archipelago's 300,000 police on standby, national police spokesman Maj. Gen. Aryanto Budihardjo said.

Security was increased around embassies and ambassadors' residences in the capital, Jakarta, and President Susilo Bambang Yudhoyono ordered the city's 11 million residents to re-register with authorities. Yudhoyono has warned that terrorists could be planning more strikes in the world's most populous Muslim nation.

Thai Prime Minister Thaksin Shinawatra ordered plainclothes security officials to popular tourist spots, warning that terrorists were "commuting and rotating around in the region."

"They have close connections and links. Their linkages come from relatives, friends and they used to go to the same schools," said Thaksin, who usually downplays the terror threat to tourism — his country's economic lifeblood.

Foreign Minister Alexander Downer of Australia, whose citizens were among those killed in Bali over the weekend as well as in the 2002 attacks, also struck a warning note.

"People shouldn't think because those bombings took place, there now won't be any bombings for another year or so, or two years," Downer told the Nine television network. "The risk is always there and the risk is significant."

The Philippines placed its 115,000-strong police force on heightened alert and said it would intensify intelligence gathering, while Malaysia tightened border security to prevent the alleged masterminds of the Bali attacks from returning home.

Nobody claimed responsibility for Saturday night's coordinated attacks, but suspicion fell on Jemaah Islamiyah, which wants to establish an Islamic state across Southeast Asia. If proved, the strikes show how dangerous the group remains despite a regional security crackdown that has arrested hundreds of alleged group members.

Analysts say the group appears to have taken on a different form, using foot soldiers from other organizations to carry out attacks. Saturday's bombers targeted two outdoor seafood restaurants on bustling Jimbaran Beach and a three-story noodle and steakhouse in Kuta, the tourist heart of the island.

The explosions occurred within six minutes on the busiest night of the week.

The bombers were wearing the explosives — packed with ball bearings and other shrapnel to maximize casualties — around their waists or in bags over their shoulders.