JOLO - A Muslim cleric has been asked to mediate in talks to free three Red Cross workers being held in the southern Philippines by Islamist rebels, an official said Thursday.

The cleric, who has not yet been named, will head a group of people from influential Muslim families from the island of Jolo, where the kidnapping took place, said Jolo Mayor Hussin Amin.

The International Committee of the Red Cross workers were kidnapped by members of the Abu Sayyaf Islamist group on January 15 while on a humanitarian mission to help inmates at Jolo municipal jail.

"This is the first move to open communications between the captors and the authorities," Amin said.

The three workers -- Andreas Notter of Switzerland, Eugenio Vagni of Italy and Filipina Mary-Jean Lacaba -- are said to be in good health and have been able to phone relatives.

The Abu Sayyaf has not made any ransom demands so far but has asked the government to allow diplomats from the hostages' countries as well as the country's vice president to negotiate with them.

The military has rejected a demand from the rebels for troops to pull out of Jolo, but has said it was prepared to launch rescue operations once all peaceful means to solve the crisis are exhausted.

In an interview with a local daily this week, Lacaba said no one has yet started talks to free them. Notter said his two colleagues had suffered severe diarrhea while in captivity, though they remained unharmed so far.

Alain Aeschlimann, the ICRC's Geneva-based head of operations for Asia, said the agency has spoken to the hostages "on a relatively regular basis."

"We've taken note of the article," he said, referring to the interview. "They are being held hostage, so we do not know the circumstances in which they spoke to the journalist."

He urged caution in discussing the situation so as not to jeopardize the safety of his staff.