PROSPERIDAD, Philippines, December 12, 2009 (AFP) - Tribal gunmen in the southern Philippines warned Friday they would massacre dozens of hostages if police made a rescue bid, as hundreds of security forces surrounded their mountain lair.

Forty-seven people remained captive in the two-day hostage drama, part of an upsurge of unrest in the Mindanao region, where a political massacre last month triggered martial law in one province.

"I will kill the hostages if police attempt to rescue them," the gunmen's leader, Ondo Perez, told an AFP reporter who accompanied a government negotiator to the remote mountain site.

Perez released 10 of his 57 hostages shortly afterwards, according to the negotiator, Josefina Bajade. Nine of those released were women and the other was a boy, Bajade told AFP.

But hopes that the 47 remaining hostages would also be quickly released faded at nightfall, with government officials saying negotiations had been suspended and would resume on Saturday.

"The negotiations have collapsed for the night. There have been no more new releases," the vice-governor of Agusan del Sur province, Santiago Cane, told reporters.

Seventy-five people were seized on Thursday from a school and neighbouring houses in a small farming village on the outskirts of Prosperidad, the provincial capital.

A recent explosion of violence in the southern Philippines comes amid increased political tension, as President Gloria Arroyo, a US ally, is due to step down next year having completed her second term.

Authorities identified the gunmen as members of the Manobo clan, and said they were wanted on charges of murder and other crimes.

Perez, carrying an assault rifle and clad in rubber boots, shorts and a tattered shirt, gave police one week to meet his demands, including lifting arrest warrants issued against his 15-man group.

He also demanded that authorities disarm a rival clan engaged in a bitter land feud with the Manobos.

Bajade secured the release of 18 hostages, mainly school children, within eight hours of the kidnapping.

The 47 still in captivity are mainly farmers and other residents of the raided village, plus the school principal, according to local officials.

They were held in an abandoned hut in a clearing of a thickly forested mountain about two kilometers (1.2 miles) from their village.

At least 400 police and army personnel were deployed on the mountain and preparing to assault the lair if commanders gave the green light, according to an AFP reporter on the scene.

Bajade said the Manobo tribesmen launched the raid to prevent police from serving arrest warrants against family members for the murder of four people belonging to the rival family.

The mass kidnapping was part of a wave of violence that has been stunning even for the southern Philippines, where Muslim and communist insurgents mix with warring clans, pirates and corrupt officials.

Islamic militants on Thursday abducted a college professor on Basilan island, which is part of the Mindanao region, a day after beheading another captive whom they kidnapped on November 10 from a logging company.

The Al Qaeda-linked Abu Sayyaf, which specialises in kidnappings-for-ransom, were holding three people in total on Basilan, the two others being from the logging firm.

Maguindanao province in Mindanao, meanwhile, remained under martial law following the massacre last month of 57 people, allegedly by the heads of a Muslim clan that had ruled the area since 2001.

The Ampatuans are accused of organising the November 23 massacre to stop a rival politician from challenging them for the post of provincial governor in elections next year.