The aid workers - Swiss national Andreas Notter, Eugenio Vagni, from Italy, and Mary Jean Lacaba, a Filipino national - were kidnapped on January 15 and are believed to be held hostage by the Abu Sayyaf, a separatist group that intelligence agencies say has ties to al-Qaeda.
Al Jazeera's Marga Ortigas reporting from the southern Philippines said a release is expected soon.
"There has been no confirmation of an exact date or time, but our sources have told us that according to those holding the aid workers, a release is imminent," she aid.
|The Red Cross workers have been held captive since mid-January [AFP]
Earlier a man claiming to be Albader Parad, an Abu Sayyaf commander, had threatened to behead one or all of the aid workers if the military launched a new attack on his group.
"Remember, if they pursue the operations and they come close to us and another firefight erupts, I will behead one of the group of ICRC[International Committee of the Red Cross] hostages," the man said in a radio interview.
Speaking to reporters in Manila, Richard Gordon, the head of the Philippines Red Cross, said he had convinced Parad in a phone call to promise to release one of the hostages if troops pull back from the area.
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 military said up to nine people, including three soldiers, were killed and dozens wounded but it said the fighting was not an attempt to free the hostages.
They said the clashes broke out when the fighters tried to break out of a military cordon around the area.
Military officials said they later found a tent belonging to the three aid workers.
The Abu Sayyaf group has been blamed for a string of high-profile kidnappings and bomb attacks, including the 2004 bombing of a passenger ferry that killed over 100 in Manila Bay.
It has kidnapped dozens of foreigners, businessmen and religious workers over the past decade and is on the US government's list of foreign terrorist organisations.