The US Government has offered a reward of up to $5m for the capture in the Philippines of leaders of the Abu Sayyaf, the Muslim militant group holding an American missionary couple and a Filipina nurse hostage.

We believe that ordinary citizens of the Philippines and elsewhere may have the information that can help bring the Abu Sayyaf terrorists to justice

US ambassador Francis Ricciardone

The US ambassador to Manila, Francis Ricciardone, said the reward would be offered for any or all of five leaders of the group, including its leader Abu Sabaya.

He appealed for those with information to phone the US embassy in the Philippines. Any reward will be decided by a US committee.

Both countries have denied earlier reports that two helicopters belonging to US troops helping the Philippines army to search for the rebels had come under enemy fire. Officials say the shots were merely blanks fired in a training exercise.

Ring-leaders

The reward is for information leading to the arrest of any or all of the following Abu Sayyaf leaders:

• Amir Khadafi Abubaker Janjalani (a.k.a. Abu Mukatar
• Jainal Antel Sali Jr. (a.k.a. Abu Solaiman)
• Aldam Tilao (a.k.a. Abu Sabaya)
• Isnilon Totoni Hapilon (a.k.a. Abu Musab)
• Hamsiraji Marusi Sali, a.k.a. Jose Ramirez

The Abu Sayyaf, now thought to number less than 100, are believed to be hiding on the southern island of Basilan with their three hostages - Martin and Gracia Burnham, originally from Wichita, Kansas, and Filipina Deborah Yap.

The Burnhams were part of a group of 20 tourists taken hostage by the Abu Sayyaf from a luxury resort last May. The rebels later beheaded the other American, Guillermo Sobero of Corona, California.

About 1,000 US troops have provided the Philippines army with training, spy planes and satellites in their search for the rebels, who claim they are fighting for a Muslim state in the south of the country.

A US missionary couple are being held somewhere in the jungle

The Philippine authorities describe them as simply bandits who regularly engage in kidnap for ransom, while the US says they have links to Osama bin Laden's al-Qaeda organisation, blamed for the 11 September attack on America.

The Philippines already has a year-long reward of $100,000 out for the capture of the five rebel leaders, but without success.

But Mr Ricciardone stressed the effectiveness of the US Rewards for Justice programme, under which the reward is offered, claiming that it had already saved many lives around the world.

"We believe that ordinary citizens of the Philippines and elsewhere may have the information that can help bring the Abu Sayyaf terrorists to justice" and the reward will encourage them to share that with the US, he said in a statement.