Prime Minister Prayut Chan-o-cha and a group of officials departed from the military airport in Don Muang on Sunday morning to take part in the 50th anniversary of Singapore's National Day.
The prime minister did not give an interview to reporters who were there to see him off at the airport. He is scheduled to return to Thailand at 11.20pm on Sunday.
Maj Gen Weerachon Sukhondhapatipak, a deputy government spokesman, said Gen Prayut and others in the group were taking with them red shirts to wear for the National Day celebrations in the honour of the host country.