Indian rebels fighting Bhutanese troops have offered to move out of their bases in the Himalayan kingdom if the army operation against them is halted.
The Ulfa leader has warned of "dire consequences"
Bhutanese soldiers have overrun several rebel bases in the south and arrested three senior separatist leaders.
Nearly 70 people are reported to have died in fighting. It is Bhutan's first campaign against the rebels.
Troops are trying to evict more than 3,000 Indian rebels from 30 of their bases inside the kingdom.
"Located on strategic heights in rugged jungle terrain, the camps are usually guarded by a series of outposts and landmines," a Bhutanese government statement said.
Plight of civilians
The three groups, the United Liberation Front of Assam (Ulfa), the National Democratic Front of Bodoland (NDFB) and the Kamtapur Liberation Organisation (KLO), have offered to negotiate their withdrawal from Bhutan.
The Ulfa has appealed to the Red Cross to intervene, to protect the lives of women and children belonging to rebel families who, they say, are caught in the fighting.
The rebels say they have lost 39 men, and another 50 members have been injured since fighting began on Monday.
At least 33 Bhutanese soldiers have been killed.
Three senior rebel leaders, Mithinga Daimary of the Ulfa and Tom Adhikary and Milton Roy of the KLO have been arrested.
The BBC's Subir Bhaumik in Calcutta says they are likely to be handed over to India.
Indian army helicopters were evacuating badly wounded Bhutanese soldiers
from remote hilly jungle locations and flying them to Indian hospitals,
report local correspondents.
Indian forces have sealed the border
The rebels changed their tactics after suffering initial losses, a Bhutanese military officer told the BBC.
"They are attacking our supply lines, they are using explosives and land
mines to obstruct our build-up in key locations," he said.
Bhutan's tiny army, barely 10,000-strong, has deployed more than half of its
soldiers in the military operation.
These groups have maintained their bases in the kingdom for the past
Thousands have died since the rebel groups took up arms.
The Ulfa is fighting for Assam's
independence from India while the NDFB and the KLO are fighting for separate tribal homelands.