Hours after parliament descended into chaos, police arrested 50 protesters who set fire to buses and taxis to try to enforce a nationwide strike called by the Maoists in protest at moves to finalise the charter.
The opposition Maoist party is trying to prevent the ruling coalition from pushing proposals through parliament without agreement before the January 22 deadline.
The Maoists say discussions should continue until final agreement is reached, even if that means missing the deadline to approve and publish the constitution.
The strike held on January 20, shut down factories, shops, schools and public transport in the Himalayan nation, which has endured prolonged political limbo since 2006 when the Maoists ended their decade-long insurgency.
The usually gridlocked streets of Kathmandu remained clear during morning rush hour as many people heeded the Maoist call to stay home in the capital, where authorities had deployed 6,000 police.
Despite extensive discussions, lawmakers have failed to agree on a charter and are widely expected to miss the January 22 deadline, further deepening disillusionment with the political process in the young republic.
Disagreements persist on crucial issues, with the opposition calling for new provinces to be created along lines that could favour historically marginalised communities such as the "untouchable" Dalit caste and the Madhesi ethnic minority.
The ruling parties and their allies have the two-thirds majority in parliament that they need to approve a constitution without Maoist support.
But the former rebels have warned of further conflict if the parties fail to take opposition views into account.
Former Maoist premier Mr Baburam Bhattarai told cheering supporters in Kathmandu that his party was prepared for a long fight to ensure "a progressive constitution".
"Weren't (these parties) the forces we fought against? They didn't need a constituent assembly, they didn't need a republic... they didn't need federalism or secularism or an inclusive democracy," he said.
Mr Akhilesh Upadhyay, editor-in-chief of The Kathmandu Post, told AFP a unilateral move towards a vote would result in "a constitution that has no credibility".
Furthermore, it would likely alienate already marginalised communities across the country, from the Madhesis in the southern plains to the Limbu minority in the east, Mr Upadhyay said.
"A constitution at any cost, accompanied by a serious risk of unrest, would be a pyrrhic victory for Nepal," he said.
Nepal has had two elections and six prime ministers since 2008, when parliament voted to abolish a 240-year-old monarchy and usher in a secular republic.
by Ammu KANNAMPILLY
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