Islamic militants abducted five workers of church-based non-government organizations in the southern Philippines, but freed three hostages hours later, the military said Tuesday.

The hostages were on their way back to Isabela City in Basilan province, 900 kilometres south of Manila, when their vehicles were blocked by Muslim Abu Sayyaf rebels in Kabangalan village in Tipo-Tipo town on Monday.

Rear Admiral Emilio Marayag said marines immediately launched search and rescue operations for the five abducted workers, who belonged to the Nagdilaab Foundation and the Christian Children's Fund.

"Abu Sayyaf rebels released three of their hostages hours later in a bid to slow down marines who were closing in on them," he said. "There has been no demand so far from the kidnappers, and the rescue operation is continuing."

Marayag identified the freed workers as Ludivina Dekit, Romeo Delos Reyes and Jun Estandarte. The remaining hostages are Esperanza Hupida and Millet Mendoza.

Father Angel Calbo, supervisor of the Nagdilaab Foundation, called for the immediate release of the remaining two hostages.

"These people are just workers helping the Muslim and Christian communities in Basilan," he said. "We are an NGO."

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.