According to Sinchew, The Civil Aviation Authority of Thailand (CAAT) announced the extension of the ban on the international flight until June 30 in order to prevent and contain the spread of COVID-19.
Photo source: blog.aci.aero
CAAT implemented the "flight ban" in early April, prohibiting all passenger flights from entering Thailand. There are exceptions for state or military aircraft, emergency or technical landing, humanitarian aid, medicine and relief flights, repatriation, and cargo aircraft.
In addition, all flights entering Thailand under the above special circumstances, all passengers and crew on board must be quarantined for 14 days according to CAAT's regulations.