The Thai government said Monday it would accept a ceasefire offer from a "Red Shirt" protest leader if their fighters end raging street battles and return to their main camp in central Bangkok, as the death toll from five days of violence rose to 37. 

The offer was made by Red Shirt leader Nattawut Saikuwa, who called the government's chief negotiator, Korbsak Sabhavasu, on his cell phone, Korbsak said. It was the first direct talks between the two sides since the fighting started Thursday, but Korbsak said it was unlikely to achieve much as the two sides still remained far apart. 

Nattawut's response was not immediately known. Calls to his phone went unanswered.

Earlier, a Thai government ultimatum passed for the thousands of protesters, who have been camping in an upscale commercial district for more than a month in a bid to force the government from power, to vacate the barricaded protest zone by 3 pm or face up to two years in prison. Meanwhile, unrest flared in various parts of the downtown area outside the barricades, with troops firing live ammunition at protesters who were lighting tires to hide their positions. The thick smoke darkened the sky.

The Red Shirts, many of whom hail from the impoverished north and northeast, are trying to unseat Prime Minister Abhisit Vejjajiva and force immediate elections.

Previous attempts to negotiate an end to the two-month standoff have failed. A government offer earlier this month to hold November elections floundered after protest leaders made more demands.

Korbsak told reporters that he talked to Nattawut for five minutes, during which the Red Shirt leader proposed a ceasefire. He said he told Nattawut that the army will stop shooting if he pulls his fighters back from the streets to the core protest site.

"If they call their people back to Rajprasong there will be no single bullet fired by the soldiers," he said, referring to the 1-square-mile (3-square-kilometer) area in central Bangkok where thousands of Red Shirt protesters are encamped.

"If he (Nattawut) is serious about solving the problem he is capable of doing it. He can simply call back his people. ... Once he calls them back who would the troops shoot at?" Korbsak said.

The Rajprasong area is encircled by troops in a wide perimeter, and protesters have spilled out into surrounding streets that have become a battleground. At least 37 people, nearly all civilians, have been killed in the violence and more than 250 injured.

The political conflict is Thailand's deadliest and most prolonged in decades, and each passing day of violence deeply divides in this nation of 65 million -- Southeast Asia's second-largest economy.

Earlier Monday, a small plane dropped leaflets urging protesters in the Rajprasong encampment to leave by 3 pm or face criminal charges and up to two years in prison.

The deadline passed without incident. It was not clear how many people left the camp, but the government said 3,000 people remained, down from 5,000 on Sunday and 10,000 last week. The numbers could not be independently confirmed.

It was unknown how many were rioting outside the main protest zone.

Some protesters commandeered a fuel tanker from a gasoline station and pushed it to the middle of the key Rama IV road that has become a battleground. The protesters tried to set it ablaze with a burning tire and fireworks, but were deterred by troops.

Also Monday, the so-called military strategist of the Red Shirts, who was shot in the head in an apparent sniper attack last week, succumbed to his injuries.

The shooting last Thursday of Maj. Gen. Khattiya Sawasdiphol had sparked the latest unrest, and his death raised fears violence could get worse.

Another Red Shirt leader, Jatuporn Prompan, said the only hope now to end the violence was intervention by Thailand's revered King Bhumibol Adulyadej.

The 82-year-old king, hospitalized since September, has remained publicly silent on the crisis, unlike decades past when he stepped in to stop bloodshed.

Authorities have not spelled out what would happen after the deadline to leave the encampment, but there are concerns it could precede a crackdown. Still, previous such deadlines have been ignored without consequences.

A previous army attempt to disperse the protesters on April 10, when they had congregated in a different area of Bangkok, left 25 people dead.

According to government figures, 66 people have died and more than 1,600 have been wounded since the Red Shirts began their protests in March. The toll includes 37 killed, almost all of them civilians, and 266 wounded since Thursday.

Days of prolonged fighting and disruption to normal city life have taken their toll on Bangkok residents. Most shops, hotels and businesses near the protest area are shut and long lines formed at supermarkets outside the protest zone as people rushed to stock up on food. The city's two mass transit systems remained closed Monday.