Police and military in the south have tightened security ahead of President Gloria Macapagal-Arroyo's visit today to Basilan province, even as Philippine officials said they feared Muslim rebels had killed one of three American hostages they are holding along with more than 20 Filipinos.

The military had said earlier it could not confirm rebel claims to have beheaded Californian tourist Guillermo Sobero, but the chief government spokesman said statements by Filipino hostages, including a Muslim cleric freed on Saturday by the rebels, suggested the American may be dead.

"From the hostages' statements, from what the ustadz said, it is likely that Sobero has been killed," presidential spokesman Rigoberto Tiglao said in Manila. "They said Sobero was separated from them and they never saw him again," Tiglao said.

Francis Ganzon, a former undersecretary of transport under Corazon Aquino, and one of three hostages released on Saturday said Abu Sayyaf spokesperson Abu Sabaya had told them that when the Malaysian ambassador joined the negotiations more hostages would be released.

"But that did not last," Ganzon said, "because we were again fired upon by the military. That enraged Sabaya." So that same night, the bandits beheaded the Peruvian American, he said. At the same time, hopes were rising of more hostages being released. Sources close to the families of the hostages told Reuters that the rebels were considering releasing two more Filipinos but gave no other details.

The sources said the guerrillas have been using a satellite phone to contact the victims' families and make ransom demands, the amounts depending on the social status of the families.

Meanwhile, a state of heightened alert was imposed in the largely Muslim province in preparation for Arroyo's visit to Lamitan town, the scene of last week's fierce fighting between military and rebel forces, that left dozens of soldiers dead and wounded.

"We are tightening security in Basilan and Zamboanga City because of the President's visit," said spokesman of the military's Southern Command, Col Danilo Servando.

Arroyo is expected to visit refugees in Basilan province. Hundreds of families, mostly ethnic Muslim, have fled their homes in the towns of Lantawan, Lamitan and Tuburan because of the fierce fighting.

Military leaders gathered at a southern military base yesterday to devise new strategies to fight Muslim extremist kidnappers who have dodged a massive army hunt for weeks on a remote island.

Military Chief of Staff Diomedio Villanueva arrived in the southern city of Zamboanga yesterday to review the situation with his generals. He also prepared tight security for President Gloria Macapagal Arroyo who was to visit Basilan island, the heart of the three-week hostage crisis, aides said.

The Presidential Security Group was also in Basilan yesterday to inspect security measures. The military will brief Arroyo on the progress of the government offensive against the small, but mostly violent, Moro rebel group still fighting for independence in the southern Philippines.