UN Secretary General Ban Ki-moon has urged protesters and the authorities in Thailand to avoid further violence after deadly clashes in Bangkok.
Mr Ban’s office said he "strongly encourages them to urgently return to dialogue".
Recent clashes between Thai troops and anti-government protesters have left 10 people dead and dozens injured.
The protesters, who want the prime minister to resign, are barricaded in a large camp in the centre of Bangkok.
Further outbreaks of violence have been reported overnight with plumes of smoke rising from sections of the city.
Troops have set up roadblocks in a wide area to stop supporters of the anti-government "red-shirt" movement from reinforcing the thousands of protesters already in the camp.
On Friday, troops fired live rounds, tear gas and rubber bullets in clashes with the protesters, who threw petrol bombs and stones at the soldiers.
"The secretary general is following with growing concern the rapidly mounting tensions and violence in Thailand," Mr Ban’s office said.
"He appeals to both the protesters and the Thai authorities to do all within their powers to avoid further violence and loss of life," its statement said.
"He strongly encourages them to urgently return to dialogue in order to de-escalate the situation and resolve matters peacefully."
The US has also urged restraint and encouraged the two sides "to find a way to work peacefully through these differences and do so in a way that strengthens democratic institutions," said state department spokesman PJ Crowley.
‘No choice’
The Bangkok authorities have cut off water and electricity to the camp in a renewed effort by the Thai government to reclaim the city centre after a two-month stand-off.
Violence escalated on Thursday after a renegade general who supports the protests was shot in the head by an unknown gunman.
Gen Khattiya Sawasdipol, better known as Seh Daeng (Commander Red), is in a critical condition and doctors believe he is unlikely to survive.
The American and British embassies were among several foreign missions closed on Friday.
At least nine people were killed on Friday and a demonstrator was shot dead on Thursday night.
More than 100 people have been wounded, reports quoting hospital sources say.
Broadcaster France 24 said its Canadian-born TV reporter Nelson Rand had been hit in the leg, hand and abdomen. He has undergone surgery and is said to be recovering.
A Thai cameraman from the VoiceTV news website and a photographer for the Thai newspaper Matichon were both shot in the leg, their news outlets said.
A government spokesman said troops had come under attack and "had no choice but to respond".
The spokesman, Panitan Wattanayagorn, said soldiers were authorised to use live rounds in self-defence, for warning shots or against armed protesters.
The military said some protesters had fired guns and threw grenades, Reuters news agency reported.
The protesters, who have adopted the colour red, have reinforced the barricades around their camp made of bamboo stakes, tyres and sandbags.
Many of the protesters support former Prime Minister Thaksin Shinawatra, who was ousted in a 2006 coup.
They want Prime Minister Abhisit Vejjajiva to dissolve parliament and call fresh elections.
He had offered polls in November – but the two sides failed to agree a deal because of divisions over who should be held accountable for a deadly crackdown on protests last month.
Mr Thaksin has called on the government to withdraw troops and restart negotiations.
Thailand’s worst political unrest in nearly two decades has now left at least 36 people dead and more than 1,400 wounded.
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