Nepal's Maoist rebels say the country's peace process and ceasefire are over.
The ceasefire has been under growing strain in recent weeks.
Violence has increased in recent weeks
Peace talks between the government and the rebels ended in deadlock last week after disagreement over the monarchy's place in the constitution.
Thousands of people have been killed since the rebels launched their campaign for a communist republic seven years ago.
"There is no significance to holding any more peace talks... or observing the ceasefire after the government failed to meet our demand for a constituent assembly," rebel leader, Prachanda, said in a statement issued on Wednesday.
The Maoists had asked for a special committee to draft a new constitution for the country, which would offer the option of abolishing the monarchy.
But the government ruled out a fresh constitution, saying the rebels must either lay down their weapons, or temper their demands to fit existing laws.
The rebels' decision to end the ceasefire follows the passing on Wednesday of a deadline by which the government was meant to have responded to their demands.
Mr Prachanda said the rebels had not closed the doors on dialogue, but more work was needed to create a "favourable atmosphere" for talks.
Plea to reconsider
In response, the Nepalese Government described the Maoists' decision as "unfortunate".
Information Minister Kamal Thapa, who is one of the government's negotiators, urged the rebels to reconsider their move.
He said the government was ready to be flexible.
Following the break-down of the latest round of talks last week, both sides voiced their continued support for the peace process.
A new date and venue for resuming dialogue was meant to have been set on Tuesday, 26 August - but no such announcement was made.
The worst violence in Nepal's recent history came when the rebels pulled out of previous peace talks in 2001.
There has been an upsurge in violent skirmishes after peace talks broke down last week over rebel demands for a special assembly to revise the constitution.
At least 14 people have been killed in fighting since Tuesday. And a former prime minister escaped an assassination attempt on Monday.