The International Committee of the Red Cross is calling for the unconditional release of three staff members kidnapped by suspected Islamic militants in the southern Philippines.
The head of the Geneva-based group's Asia operations, Alan Aeschlimann, urged the abductors to return the captives safe and sound.
He added that their colleagues hope to hear their voices again soon and that they remain unharmed.
The three have contacted the Red Cross several times since they were kidnapped by suspected Abu Sayyaf gunmen on January 15. Their last phone call was on Monday.
The head of the Philippines' national police told reporters that he has received information that the victims remain unharmed, but declined to give more details.
Philippine authorities and another militant group that has agreed to help with the search said the kidnappers handed the three aid workers over to Abu Sayyaf after the abduction took place last week.
The Red Cross workers were seized just outside a jail, where they met with officials to discuss improving living conditions.
Local media are reporting rumors of a possible ransom. Red Cross officials and the Philippine government both said they will not pay a ransom.
The kidnapped workers have been identified as Andreas Notter of Switzerland, Italian Eugenio Vagni and Jean Lacaba of the Philippines.
Some information for this report was provided by AFP and Reuters.