The FCO said Thursday that tensions near the British Embassy in Bangkok are high and there are major escalations in the level of violence in the Thai capital.
"You should avoid this area and if violence breaks out remain indoors and monitor the media and this travel advice," a warning read. "British nationals may wish to consider if it is essential for them to travel within central Bangkok."
Thai military forces descended on a protest camp of the so-called Red Shirt opposition group, calling on people to leave the area in the capital city. The BBC reports that gunfire erupted after a deadline to clear the camp expired.
A Thai military leader backing the Red Shirt protesters was shot during Thursday's unrest, the BBC added. Protesters are calling on the Thai prime minister to dissolve the government and call new elections.
Street lights, meanwhile, were shut off in an effort to confuse the protesters, though BBC reporters said the situation was chaotic.
"We advise against all but essential travel to the city of Bangkok, in view of the continued political unrest," the FCO warned.