The Philippine government on Saturday urged residents of a southern province to help authorities track down kidnappers of two humanitarian workers abducted by suspected Islamic militants.

The hostages - Esperanza Hupida and Millet Mendoza - were among five workers of a church-based non-governmental organization abducted on September 15 in Tipo-tipo town in Basilan province, 900 kilometres south of Manila.

The three other workers were freed hours later by the kidnappers, suspected to be members of the Abu Sayyaf group.

Presidential Press Secretary Jesus Dureza said Hupida and Mendoza "do not deserve this fate" and all efforts must be exerted to rescue them safely.

"The communities whom they have served and who value their work and sacrifices must move as one with our authorities to help resolve this unfortunate incident," he said.

But Dureza stressed the government's policy against paying ransom to kidnappers.

"The government maintains its no-ransom policy," he said. "But all efforts must be exerted to bring home safely our NGO workers who have risked their lives in the service of the suffering people of the area."

"It is so tragic that terrorist elements target as victims the very people who are out there to serve their own communities," he added.

Basilan is a stronghold of the Abu Sayyaf, a Muslim rebel group blamed for kidnapping-for-ransom activities and terrorist attacks. It has also been linked to the al-Qaeda terrorist network and the regional Jemaah Islamiyah group.