SANAA (AFP) -- The kidnappers of four French tourists threatened on Tuesday to kill their hostages if Yemeni authorities use force to try and free them, a tribal source told AFP.

"The kidnappers threatened to kill their hostages if authorities use any kind of military action to forcefully free the French hostages," the source said on condition of anonymity.

The announcement came after negotiations with authorities had stalled, the source said.

The captors have been holding the four French since Sunday in a mountainous region of the southeast Shabwa province, and are demanding authorities release members of their tribe in exchange for the hostages' release.

"A tribal delegation and representatives of local authorities agreed with the kidnappers to hand over four children of three local leaders and the head of the detention camp in exchange for the release of the French hostages," the source said.

Upon release of the French hostages, the children would then serve as bargaining tools for the release of jailed members of their tribe.

Negotiators also promised the kential election on September 20, the source said.

"But the head of the detention camp refused at the last minute to hand over one of his sons to the tribe that kidnapped the French. The kidnappers in turn refused to free the French hostages because they no longer considered the deal was credible or serious," the source said.

They then "threatened to kill the hostages" in case any force is used against them.

A tribal source said the kidnappers were members of the Al-Abdullah bin Daham tribe which also abducted a German family of five last December.

The tribesmen abducted the four French tourists in protest at the authorities' failure to keep promises to release jailed members of their tribe in exchange for freeing the German family at the time, the source said.

The jailed tribesmen are being held over a vendetta against members of a rival tribe, the source added.

"We are disappointed that the negotiations were not successful this evening," a French diplomat in Sanaa was quoted as saying by the SABA news agency. "We trust our Yemeni partners will restart talks tomorrow." A spokesman for the Yemeni interior ministry also said negotiations would continue "in view of freeing the hostages as soon as possible" and assured that the four were "iafety of the tourists."

Armed tribesmen have repeatedly seized Westerners to put pressure on the central government to respond to their demands, and the latest abduction came 10 days before Yemen goes to the polls to elect a president and new local councils. President Ali Abdullah Saleh's ruling General People's Congress condemned the abduction in a statement posted on its website, saying it "undermined Yemen's reputation and will have negative effects on the economy, tourism and Yemen's relations with other countries."

Combating violence is one of the themes of the veteren 1991 and 20 01, more than 200 foreigners were kidnapped in Yemen.

The hostages have generally been released unharmed, but three Britons and an Australian seized by Islamist militants were killed when security forces stormed their hideout in December 1998.