Thailand's King Bhumibol Adulyadej speaks during a ceremony to celebrate his 83rd birthday at the Grand Palace in Bangkok Dec 5, 2010. [Photo/Agencies]

BANGKOK - Thailand is marking the 83rd birthday of King Bhumibol Adulyadej, the world's longest reigning monarch.

Bhumibol delivered his annual birthday speech Sunday, sounding what has become his usual call for unity to keep the country happy and prosperous in the face of the sometimes violent political conflict it has faced in recent years.

The king made his brief remarks at the ceremonial Grand Palace in a slow and rasping voice. Thousands of flag-waving citizens cheered his car's journey from Siriraj Hospital, to which he was admitted in September 2009 with a lung inflammation. There has been no detailed explanation of his extended stay.