KATHMANDU, Aug 21: Maoist rebels who have cut off Nepal's capital for four days pledged on Saturday to expand their blockade to the Tibetan border as fresh violence left six people dead.

The rebel threat came a day after the government appealed to the Maoists to call off the blockade and resume negotiations to end the increasingly deadly insurgency which has claimed nearly 10,000 lives since 1996.

The Maoists have not physically surrounded the city but have warned transporters not to enter the Kathmandu Valley, leading to a siege mentality that has sent some prices soaring in local markets.

The rebels announced they would start a new blockade next Saturday to prevent transport from the only land connection into Tibet, the Kodari pass, 115 kilometres north of Kathmandu.

"This blockade will stop all vehicles from moving to the frontier," read a statement from Devi Khadka, also known as Asita, who is the Maoist general secretary for three districts near the border.

While the blockade of the Tibetan border is unlikely to have an immediate impact on Kathmandu, it could hinder the growing overland trade with China and for tourists who cross the Himalayas into Tibet.

The Maoists are fighting to abolish the monarchy and draw inspiration from China's founder Mao Zedong, although they are disavowed by Beijing, which this month hosted Nepal's Crown Prince Paras.

In the latest violence in the besieged Kathmandu Valley, suspected Maoists Saturday gunned down a police sub-inspector at Chabahil on the capital's outskirts.

Prithbi Bahadur Singh, the head of a police guard posted to the Gopi Krishna cinema, was hit in the chest by two bullets when he entered the theatre's front yard, a police official said.

The official had no explanation as to the motive. The Maoists have regularly targeted businesses that do not pay "donations" to the rebel cause.

An army statement said troops shot dead five Maoists in separate incidents Friday.

The dead rebels included "bomb-making specialist" Bharat Raj Giri, who was gunned down as troops spotted him setting up a landmine in the eastern Sindupalchak, the statement said.

The Maoists have not forced the closure of transport, offices or shops inside Kathmandu, which has stayed tranquil with the bylanes thronged by pedestrians and foreign tourists.

But residents worry that a prolonged shutdown could lead to a shortage of fresh produce, which mostly comes from outside the Kathmandu Valley.

The government has appealed for the Maoists to call off the blockade and return immediately to the negotiating table.

Information Minister Mohammad Mohsin promised to meet a key guerrilla demand to investigate the whereabouts of an unspecified number of leftist activists who have disappeared. He said the results would be made public within a month.

There has been no direct response to the statement by the Maoists, whose leadership lives in hiding.

But the government did not budge on another major Maoist demand: that they be delisted as a terrorist group. The group was given the terrorist label after rebels broke a ceasefire last year, ushering in a new bloody phase of the insurgency.

The Maoists launched the blockade after shutting down 24 top national companies through threats, including a bombing at a leading Kathmandu hotel.

The rebels on Friday issued similar threats to six businesses in Nepalgunj, the southwestern city on the edge of Maoist-controlled territory, said Sachit Agarwal, chairman for the Federation of Nepalese Chambers of Commerce and Industry in the Indian border town.

One of the six firms, which already closed, was the Sneha Hotel, which hosted the last round of failed peace talks between the government and Maoists in August last year.

The owner of the hotel, Bhabani Rana, is a relative of Queen Komal and sister-in-law of Prime Minister Sher Bahadur Deuba. -AFP