There is increasing tension in the Thai capital, Bangkok
Britons have been warned by the UK government that they should avoid all but "essential" travel to Bangkok.
The Foreign Office gave its travel advice relating to Thailand's capital because of the risk "that violence could break out without warning".
It follows a series of blasts near a massive encampment of anti-government protesters in Bangkok's business district.
A number of people are reported killed or injured in the blasts.
The Foreign Office said in a statement: "This advice reflects our concern for the safety of British nationals planning to travel to Bangkok, given the risk that violence could break out without warning during the increasingly volatile political crisis.
"The situation is changing on a daily basis, and we recommend that British nationals living in Thailand or travelling to the country check the travel advice on the Foreign Office website regularly for details of further developments."
Thai Army spokesman Col Sansern Kaewkamnerd said five M-79 grenades had been fired in the latest attack.
Three fell through the roof of the Saladaeng Skytrain station, along Silom Road, the centre of Bangkok's business district, he said.
A fourth exploded on the pavement near the five-star Dusit Thani Hotel and the fifth near a bank, he added.