The US and UK ambassadors to Thailand have spoken to the prime minister and the opposition leader to encourage them to enter a restrained and peaceful dialogue.
US State Department spokeswoman Jen Psaki said the US deeply regrets the loss of life in Bangkok due to politically motivated violence and is concerned about the continuing political tension.
She said US ambassador Kristy Kenny recently spoke to Prime Minister Yingluck Shinawatra and opposition leader Abhisit Vejjajiva to encourage peaceful dialogue and restraint.
She said Ms Kenny continued to encourage all parties to work together to resolve their differences.
However, the US is advising US citizens in Thailand to avoid areas with demonstrations and to exercise caution.
"We condemn violence as a means to achieve political objectives and urge all sides to exercise restraint and respect the rule of law," said Ms Psaki, adding the US is following the situation closely.
She said peaceful protest and freedom of expression are important aspects of democracy. Violence and seizure of public property, however, are not acceptable means of resolving political differences.
"We firmly believe all parties should work together to resolve differences through peaceful dialogue in ways that strengthen democracy and the rule of law," Ms Psaki said.
In addition to the US, a source said the UK ambassador Mark Kent also met both Ms Yingluck and Mr Abhisit on Friday to discuss the situation.
The source said the UK trusts that all sides will work together for the national interest and the future of the country.
"The UK, in line with other members of the international community, hopes that all sides will use peaceful methods and dialogue to find a way forward," Mr Kent said.
The UK viewed the right to peaceful protest as an inherent part of freedom of expression, which should be guaranteed in a democracy, he said.
"There should be no place for use of violence or undemocratic methods, including the unsanctioned occupation of property," Mr Kent said.