A hardline faction within Nepal's governing Maoist party has said it is breaking away to form a separate party.
The leader of the new grouping said the split was happening because the party's leadership had "annihilated the achievements" of the 10-year civil war which ended in 2006.
The break-up comes as Nepal is still struggling to implement a peace deal since the end of the war.
Correspondents say it will push the country into more uncertainty.
Parliament dissolved in chaos last month after repeatedly failing to agree a new constitution. National elections are due in November.
One of the breakaway faction leaders, Khadga Bahadur Bishwakarma, said the new party was opposed to Pushpa Kamal Dahal, also known as Prachanda, who led the Maoists in war and carried them to elected power in 2008.
"When we entered into peace, there was a challenge to retain the party's revolutionary spirit," Mr Bishwakarma said.
"Until a couple of years ago, Prachanda was clearly allied with us, but he deviated from it. After all sorts of attempts, we concluded that there's no alternative but to form a new party."
Breakaway leader Mohan Baidhya criticised Mr Dahal and Maoist Prime Minister Baburam Bhattarai for their failure to draft a new constitution and for their failure to ensure that former Maoist fighters were integrated into the army "in a respected manner".
Mr Baidhya said the unity in the party was still possible if Mr Dahal and Mr Bhattarai "rectify their past mistakes".
He also urged "revolutionary forces" to join the new party which was "a beginning of a new chapter it the country".
Mr Bishwakarma said the breakaway faction of the Unified Communist Party of Nepal (Maoist) would be called the Communist Party of Nepal - Maoist.