He said the safety of the International Committee of the three aid workers - Swiss Andreas Notter, Filipino Mary Jean Lacaba and Italian Eugenio Vagni - was the government's "paramount concern".

Earlier this week a series of intense clashes broke out on the southern island of Jolo between soldiers and fighters thought to be holding the hostages.

The fighting left at least three soldiers and three fighters dead.

Military officials said they later found a tent belonging to the three aid workers.

On Wednesday a man claiming to Abu Sayyaf commander Albader Parad telephoned a Philippine TV station to say the three Red Cross hostages were alive, but that their safety was at risk if government forces kept up their offensive.