Thai authorities say Mr. Sam Rainsy is not allowed to enter Thailand on the grounds that his presence and public speech could create trouble.
The Sam Rainsy Party (SRP) spokesman in Phnom Penh says Mr. Rainsy is due to address the Foreign Correspondents Club in Bangkok on the political deadlock in Cambodia.
Mr. Rainsy arrived in Bangkok from Singapore late Wednesday but was not allowed to leave the airport and instead flew on to Paris.