UN rights chief Navi Pillay said Bangkok was in danger of spiralling out of control, after five days of violence which has seen 37 people killed.

She spoke a day after protesters called for UN-backed talks to end the crisis - a move rejected by the government.

A protest leader and the government's negotiator had a five-minute phone call earlier but could not agree a truce.

Ministers say the protesters must leave their makeshift camp in the centre of Bangkok before talks can commence.


Map of protest areas in Bangkok

Bangkok clashes: Map
In pictures: General buried

They set a deadline of 1500 local time (0800 GMT) for protesters to leave - but few of the 5,000 protesters camped in the so-called red-zone heeded the ultimatum.

The protesters insist that government troops must lift their blockade of the red-shirt camp before any negotiations.

In a statement, Ms Pillay said: "I urge leaders to set aside pride and politics for the sake of the people of Thailand.

"To prevent further loss of life, I appeal to the protesters to step back from the brink, and the security forces to exercise maximum restraint in line with the instructions given by the government."

The demonstrators, who want Prime Minister Abhisit Vejjajiva to step down, have been occupying large areas of the city since mid-March.

A protester throws wood on to a fire in Bangkok, 17/05
Fires set by the red-shirts have become a symbol of their protest

Sporadic outbreaks of unrest have accompanied their protest, including an attempted crackdown by security forces in April that left 25 people dead.

Violence again broke out last Thursday, and soldiers are now openly using live ammunition; sniper fire has been reported.


RED-SHIRT PROTEST
14 Mar: Red-shirts converge on Bangkok, occupy government district
16 Mar: Protesters splash their own blood at Government House
30 Mar: Talks with government ends in deadlock
3 Apr: Occupy Bangkok shopping district
10 Apr: Troops try to clear protesters; 25 people are killed and hundreds injured
13-17 May: 36 killed in Bangkok clashes

Protests day by day
In pictures: Bangkok violence
Thai protests: Eyewitness accounts
Obituary: 'Commander Red'

The authorities say they are targeting "terrorists" who have infiltrated the protesters' ranks, but TV footage has shown unarmed protesters being shot in the streets.

While the majority of the red-shirts are conducting their protest peacefully, some have been building barricades of tyres and setting them alight. Witnesses say others are armed with guns.

Late on Monday, the two sides held what is believed to be their first direct talks since the latest unrest broke out.

The government's chief negotiator Korbsak Sabhavasu said red-shirt leader Nattawut Saikuwa had called him and asked for a ceasefire.

But Mr Korbsak told the Associated Press news agency that nothing had been agreed.

On Monday, protests spread outside the capital with a military bus torched in Chiang Mai and demonstrations in two other northern towns.
Many of the protesters are from poor rural areas in the north, where support is still strong for former Prime Minister Thaksin Shinawatra, who was deposed in a 2006 coup.

The protesters say the current government is illegitimate, having come to power in a parliamentary vote after a pro-Thaksin government was forced to step down in December 2008 by a Constitutional Court ruling that it had committed electoral fraud.