Cambodian troops and Khmer Rouge defectors began moving into northern mountains on Monday hunting for infamous former guerrilla chief Pol Pot and the crippled rebel group's current leaders.

The military said more than 3,000 Khmer Rouge had defected to the government in recent weeks but the exact whereabouts of Pol Pot, who was responsible for the deaths of more than a million Cambodians during his 1975-79 "killing fields" rule, was unknown.Government forces and Khmer Rouge defectors were moving toward an area on the Dongrek escarpment, which forms Cam-bo-dia's northern border with Thailand, where Pol Pot and the remnants of the rebel group were believed to be, commanders in Anlong Veng said.

But deputy armed forces chief General Meas Sophea said he believed Pol Pot might have crossed into Thailand. He said Khmer Rouge military strongman Ta Mok was believed to be in a Thai border village called Ban Sangam.

"Ta Mok is now in Ban Sangam and I believe Pol Pot and other leaders are with him," Meas Sophea told reporters.

Thailand has strongly denied that Pol Pot or any Khmer Rouge leaders were on its soil.

Anlong Veng was the Khmer Rouge "capital" until late March when the rebels began to mutiny and join the government.

Pol Pot, now in his 70s and in poor health, was purged by his comrades last year and sentenced to life under house arrest after he lost a power struggle with Ta Mok.

That struggle was sparked by attempts by then co-premier Prince Norodom Ranariddh to strike a ceasefire with the rebels.

Anlong Veng was quiet and largely deserted on Monday though intermittent explosions could be heard from the north as a government tank fired into an area of the Dongrek escarpment called Mountain 200.