Acting president Chokechai Panyayong said the pilots of flight TG507 had been told to return to Suvarnabhumi after leaving the Bangkok airport at 2.10pm due to safety concerns.
The Airbus A330-300 aircraft returned to Suvarnabhumi at 5.06pm, he added.
The flight with 250 passengers on board, including two Thais, and 16 crew members was scheduled to arrive in Karachi at 5.10pm (7.10pm Thailand time).
THAI is closely monitoring the situation at the Karachi airport before deciding whether to end flight cancellation to the country, he added.
The decision followed a new attack by Taliban gunmen at a security post outside the Karachi airport on Tuesday.
The latest assault on the airport raised further questions about the authorities' ability to secure key facilities in the face of resurgence.