Efforts to dislodge Khmer Rouge leaders from their final mountain stronghold could take weeks, military officials and analysts have warned. Khmer Rouge commander Ta Mok and former leaders Pol Pot and Khieu Samphan are now believed to be holed up along an escarpment near the Thai border after Cambodian troops pushed them north from their Anlong Veng base. The Dongrek mountain range is within four kilometres of the Thai border. 'Their new area seems to very well fortified indeed, and in the short term could prove very tricky to invade,' one Thai military source said. 'They have prepared this area very well for a final defence.' Defections from Ta Mok's ranks have spiralled in recent weeks, leaving the one-legged leader known as 'the butcher' with 200 to 500 crack troops. 'Even with so few troops they could still hold out for some time,' one Western military attache said. 'It is very difficult terrain and they know it well.' Another smaller group may have teamed up with Cambodian royalists near their base to the south at O'Smach. Government forces were reportedly holding back from an all-out attack on the Dongrek ridge, hoping they could persuade the 300 or so fighters to turn on their leaders. Ta Mok has been holding Pol Pot prisoner since he was denounced last July after allegedly ordering the killing of former colleague Son Sen and his family. Thai officials yesterday denied the Khmer Rouge leadership had formally sought refuge in Thailand. The Far Eastern Economic Review said General Khem Nuon, the commander of Ta Mok's forces, had asked the magazine's Nate Thayer for advice on how to hand Pol Pot over to an international tribunal. It said Thayer suggested contacting the Red Cross. The general, interviewed on the Thai border on Saturday, said he was holding Pol Pot a few kilometres inside Cambodia.