Kathmandu, Aug 8 - As negotiations between Nepal's Prime Minister Madhav Kumar Nepal and Maoist chief Pushpa Kamal Dahal Prachanda failed Saturday, the former guerrillas vowed to keep up their siege on parliament -- a move that could derail the promulgation of a new constitution next summer.

'We are ready to call off our protest if the prime minister agrees to create a conducive atmosphere in parliament for a debate,' former premier Prachanda told the media before departing on a 10-day trip to Britain.

However, he said it would not be possible.

The Maoists, whose eight-month-old government fell in May after locking horns with army chief Gen Rookmangud Katawal, have been since then seeking a debate in parliament on the issue.

Soon after the fall of the Prachanda government, the Maoists began a blockade of parliament. They lifted the siege after two months only after the prime minister's assurance that their demand would be addressed.

However, on Friday, the former rebels said the one-month grace period given by them to the government had expired without any resolution and reimposed the blockade. In addition, they have also announced street and mass protests for a month that are likely to throw the administration off gear.

The original bone of contention, Gen Katawal, has emerged unscathed in the battle and is due to retire next month.