The International Crisis Group (ICG), an independent non-governmental organisation, said on Tuesday that Nepal is at risk of more turmoil if it fails to address the demands for greater representation of the ethnic Madhesis group in the new constitution.
Ethnic Madhesis have been protesting for months against Nepal's new constitution.
At least 50 people have been killed in the protests since September in Tarai, or Madhes, a region in Nepal's southern plains bordering India.
They say the new constitution unfairly divides the Himalayan country into seven states with borders that cut through their ancestral homeland. They want the states to be larger and to be given more autonomy over local matters.
Many of them want the region, which is home to half of the country's 28 million people, to become an autonomous state within Nepal.
According to latest published report of ICG, there are social discontent and fruitful negotiations between Madhesis and the parties that represent them.
"Forcing acceptance of a flawed constitution could end the political transition and trigger unmanageable new conflict," the ICG said.
Information and Communication Minister Sherdhan Rai criticised the report, saying it is "unnecessary".
"We are ready to negotiate and address genuine demands of the Madhesis," he said.
But Upendra Yadav, from Madhesi Front which organised protests said "Lasting peace and stability are impossible without addressing our demands”.
Talks between the protesting groups and the government have made little progress, but both sides say they will continue talking.