The group has been holding the International Committee of the Red Cross (ICRC) workers for more than two and a half months.

The two foreigners being held are Andreas Notter, a Swiss national, and Eugenio Vagni, an Italian.

Hostage freed

A third hostage, Mary Jean Lacaba, was set free on Thursday.

Government officials picked up Lacaba, a Philippine engineer, in a remote village on Jolo after her captors told them where to find her.

The three ICRC workers were kidnapped on January 15 while heading to a local airport after visiting a water-sanitation project at the provincial jail.

Abu Sayyaf, which is alleged to have al-Qaeda links, had previously said it would behead one of the ICRC workers if Philippine troops did not retreat by Tuesday.

The military made a partial withdrawal from five towns on Jolo earlier in the week before again redeploying around the group's camp and declaring a state of emergency after the deadline on Tuesday.

Abu Sayyaf has beheaded hostages in the past, including an American in 2001 and seven Filipinos in 2007.

The group, which is also said to have links to the regional Jemaah Islamiyah group, has been blamed for the worst attack in the Philippines' history, in which a ferry in Manila Bay was bombed in 2004, killing 100 people.

The US government has placed the group, which is believed to have about 400 fighters, on its list of terrorist organisations.