Muslim militants have again threatened to harm their 21 American and Filipino hostages and attack Christian villagers in retaliation for a massive government crackdown, radio stations reported yesterday.

The Abu Sayyaf spokesman Abu Sabaya called several radio stations in the southern city of Zamboanga on Monday to issue the threats but was not put on air, they said. The hostages, including U.S. Christian missionary couple Martin and Gracia Burnham of Kansas, are being held on the nearby island of Basilan.

Abu Sabaya also warned the rebels would kill Christian civilians in retaliation for the crackdown on their supporters ordered by President Gloria Arroyo two weeks ago. If the military is capable of arresting Muslims, "we are also capable of executing Christian civilians", Sabaya was quoted as saying by a radio station.

The rebels had executed four Filipino captives and claimed to have beheaded a third American hostage, Guillermo Sobero of California, although his remains have not been found.

Armed forces spokesman Brigadier General Edilberto Adan said they would hold Abu Sayyaf responsible for any crimes committed against hostages or civilians. "We will not stop the crackdown until we get (Sabaya) and all his followers," Adan said in Manila.

Arroyo has given the military powers to detain suspected Abu Sayyaf rebels and those giving them shelter in a bid to end the two-month old hostage crisis. On Monday, troops arrested three Abu Sayyaf members in Basilan and on nearby Jolo island.

Over 90 suspected rebels and their supporters have been detained so far. Of the total, 46 have been formally charged with kidnapping and illegal possession of firearms, while the others remain under interrogation.

Divine Montealegre, whose sister Angie is one of the hostages, yesterday pleaded with the Abu Sayyaf to allow the captives to contact their relatives to assure them they were alive. "If only they could call so we can know what is their condition. We cannot sleep from always worrying about our relatives," Divine said over Zamboanga radio DXRZ.

The military in Basilan has stepped up the training of local villagers as militiamen to defend their communities from attacks by the Abu Sayyaf despite limited resources. Three militiamen were snatched by the rebels on Saturday.

The Abu Sayyaf seized the Americans and 17 Filipinos from a Philippine resort on May 27 and brought them to Basilan. Several had been rescued or freed, allegedly after ransom payments, but more hostages were seized as the rebels retreated into Basilan's hinterlands to flee 5,000 soldiers deployed by Arroyo.