The Foreign Office also urged tourists to follow travel advice after army chief General Prayut Chan-O-Cha announced the putsch on live TV, following months of political unrest.
"We are concerned at the announcement of a military coup in Thailand and are following developments closely," the Foreign Office said in a statement to AFP.
"We urge all sides to put aside their differences, and adhere to the values of democracy and the rule of law. This is clearly in the interests of the people of Thailand."
French President Francois Hollande earlier condemned the coup but international reaction has otherwise been muted so far.