UN Secretary General Ban Ki-moon has urged protesters and the authorities in Thailand to avoid further violence after deadly clashes in Bangkok, BBC reported.
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 16 people dead and scores 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.
UN head Ban Ki-moon urges end to Bangkok clashes
