Thai king's illness sparks anxiety "failing for long-awaited radio speech"

Last year, the king was hospitalized for more than three weeks for symptoms of a stroke and a colon infection. He also has a history of heart trouble and was operated on in 2006 for a spinal problem.

The question of royal succession has long weighed heavily on Thai politics, and ordinary Thais but probably never more than now.

Although a constitutional monarch, Bhumibol built up his great power through decades of work on behalf of the poor, charisma and political astuteness.

His 56-year-old son, Prince Vajiralongkorn, has nowhere near the king's talents, stature or moral authority. There is concern that Vajiralongkorn, who has married three times and fathered seven children, will have difficulty living up to Bhumibol's record of hard work and diligence.

Sirindhorn, 53, who could technically also succeed her father, is talented and highly popular but said to lack political savvy. There is also almost no historical precedent for a woman becoming the country's ruler.

The royal crisis could not have come at worse time for Thailand, as it struggles to recover from an anti-government campaign by the People's Alliance for Democracy.