Thimphu, Jan 1 (IANS) Bhutan has sounded a massive security alert after the killing of four forest rangers in a powerful landmine explosion by Nepal-based Maoist guerrillas, officials here said Thursday.A Royal Bhutan Police spokesman said the explosion took place near Singye village in the southern Bhutan district of Sarpang late Tuesday.

“Six Bhutanese forest rangers were returning to their camp at village Phibsoo from Sarpang town after shopping when the tractor they were travelling in hit a landmine planted on the road,” a statement by the Royal Bhutan Police said.

“After the explosion, four foresters were shot by the militants and later their dead bodies were dragged near the tractor and set on fire,” the police statement said.

The rebels decamped with two rifles with ammunition from the dead rangers. Two forest rangers managed to survive the attack but were seriously injured.

“The attack could have been the work of the Communist Party of Bhutan based in Nepal,” the police statement said.

The Communist Party of Bhutan is largely composed of Bhutanese ethnic Nepali refugees based in Nepal and has been fighting for the restoration of democratic rights of the refugees and waging a violent campaign opposing the monarchy and the newly elected government in the Himalayan kingdom.

The country had witnessed a pro-democracy agitation in the 1990s, with a section of Nepali-speaking residents in its southern parts rising in revolt against the monarchy.

The crackdown that followed led thousands of Nepali-speaking people from southern Bhutan to flee to Nepal. Now, an estimated 100,000 people are sheltered in relief camps.

In 2008, Maoist guerrillas of the Communist Party of Bhutan triggered at least a dozen explosions in the otherwise peaceful nation that made a historic shift from monarchy to parliamentary democracy last year. Bhutanese security forces in May 2008 killed five Communist Party of Bhutan guerrillas and captured 17 others in an operation.

“We have intensified security operations in the area where the explosion took place and taking all possible steps to ensure that those responsible for the attack are nabbed,” a senior Bhutanese police official said.