An explosion was heard at Supachalasai stadium, where supporters of United Front of Democracy Against Dictatorship (UDD) gathered to listen to ex-premier Thaksin Shinawatra's phone-in speech, on Saturday afternoon.
According to initial report, police believed a giant fire-cracker was thrown into the venue. No one was injured.
More than 20,000 UDD members already gathered there. About 1,000 police were deployed there to tighten security.
In the morning, a group of vocational students clashed with UDD members. There were no injuries.
