An estimated 90 to 120 militants have been killed and most of their camps demolished by the Bhutan Army in its operation against Indian insurgents based in that country, GOC-in-C Eastern Command Lt Gen J S Verma said in Kolkata on Thursday.

"The morale of the ultras has been on the lower side for the last few days and they are low on ration and poorly fed. They (militants) can't survive and will have to give up sooner or later," he told newspersons at the Eastern Command Headquarters in the first official briefing on the status of the four-day old onslaught on the insurgent groups inside the dense forests of southern Bhutan.

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He said casualties on the Royal Bhutan Army side were "not high and within acceptable limits of only six to seven. The Bhutan Army is an organised body of troops, well-equipped and well-trained."

The RBA assault on the United Liberation Front of Asom (ULFA), National Democratic Front of Bodoland (NDFB) and Kamtapur Liberation Organisation (KLO) started on December 15. Since then, a number of their camps inside Bhutan were destroyed.

Lt Gen Verma said the military assault by the RBA personnel was concentrated mainly north of Samdrup Jongkhar where most of the militants' camps were located.

Two ultras trying to escape the assault were nabbed by the Indian Army near Kokrajhar in Assam while two others were caught sneaking into Arunachal Pradesh.

Most of the ultras flushed out of their camps and now hiding in the jungles, were waiting for "a direction from their leadership. The rebels will see the writing on the wall. With their resources depleting and no escape route, they should surrender and join the mainstream," he said.

He ruled out the possibility of rebels escaping to north Bhutan saying the conditions there are cold, difficult and the area is sparsely populated.

Referring to the ULFA's appeal to Bhutan's monarch for a ceasefire, Lt Gen Verma said the Bhutan government "will take the offensive to its logical conclusion."

"I must clarify that the Indian Army is not providing artillery to the RBA. There is no truth in reports that the Indian Army has crossed over into Bhutan's territory to engage the rebels in encounters.