King Norodom Sihanouk (search) has abdicated because of poor health and has asked the people of Cambodia (search) to begin a search for a successor, the head of the National Assembly said Thursday.

The king, 81, made the announcement in a letter from Beijing. The note was read to the National Assembly early Thursday by his son, Prince Norodom Ranariddh (search), who is also head of the assembly.

"According to the statement that I have received and just read, his majesty has already abdicated," he told reporters, describing the news as "very regretful."

Ranariddh said leaders of the country's ruling coalition planned to "to beg" the king to stay on as monarch, and that he would join Prime Minister Hun Sen and Chea Sim, acting head of state, in seeking permission to visit Sihanouk in Beijing.

Sihanouk had been scheduled to return home Thursday, Ranariddh said.

Hun Sen has left for Vietnam to attend a summit between Asian and European leaders in Hanoi, the Asia-Europe Meeting.

Cambodia's monarch is not selected according to heredity, but the candidate must have a royal bloodline. Ranariddh has been considered a candidate for the throne in the past, but has said he is not interested in filling that role.

Sihanouk has been an influential figure in Cambodian politics for more than half a century, leading the country to independence from French colonialism in the 1950s.

He left Cambodia in January after trying and failing to end the feuding among the country's political parties that followed inconclusive elections in July last year. In frustration over the squabbling, he threatened several times to abdicate.

The king's statement asked the country to form a nine-member throne council — as set in Cambodian law — to consider the next monarch. The council would include leaders such as Prime Minister Hun Sen.

The statement was also posted on Sihanouk's Web site, where he often posts handwritten messages in French about current affairs. With the statement was a Sept. 4 letter jointly signed by Hun Sen and Ranariddh, who are partners in the current government, proposing another prince, Norodom Sihamoni, "to be the future king."

Sihamoni, 51, is Sihanouk's son with Queen Monineath.

In the statement, the king asked that he be allowed to "retire" because of his fragile health, saying that doctors have detected a "new and serious ailment" in his stomach. The letter did not elaborate.

"I ask all compatriots to please allow me to retire," the king's letter said.