The Geneva-based International Committee of the Red Cross (ICRC) said on Saturday that three workers kidnapped on a southern Philippine island were still alive.
Spokeswoman Anna Nelson said the three telephoned colleagues on Friday, a day after they were abducted by motorcycle-riding gunmen on southern Jolo island, and said they were unharmed.
She gave no other details, but Richard Gordon, head of the Philippine National Red Cross Society, said they had "proof of life, but no demands, so far".
Jolo island is a known stronghold of the al-Qaida-linked Abu Sayyaf, notorious for beheading their hostages and on a US list of terrorist organisations.
American soldiers were providing noncombat "assistance and advice" to Philippine forces on the current kidnapping, according to a US military official, who spoke on condition of anonymity because he was not authorised to speak to the media.
The US-trained Philippine troops searching for the hostages in the jungles of Jolo have been hampered by monsoon rains and thick vegetation.
Nelson said the ICRC was continuing its operations in other areas in the southern Mindanao region affected by fighting between government troops and Muslim separatist rebels.