Phnom Penh: Cambodia’s King Norodom Sihanouk has abdicated, citing poor health, and asked the country to begin searching for his successor, the head of the National Assembly said Thursday.

Sihanouk, 81, announced his retirement in a letter sent from Beijing which his son, Prince Norodom Ranariddh, read to the legislature Thursday.

“According to the statement that I have received and just read, His Majesty has already abdicated,” Ranariddh told reporters, adding that the news was “very regrettable and shocking for all Cambodians who love him and regard him as sacred.”

Sihanouk has repeatedly threatened to step down following inconclusive elections in July last year, expressing frustration at squabbling between Cambodia’s main political parties.

Ranariddh said leaders of the ruling coalition planned “to beg” the king to stay on as monarch. He said he would join Prime Minister Hun Sen and acting head of state and ruling party leader Chea Sim in seeking permission to visit Sihanouk in Beijing.

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

Hun Sen was in Vietnam Thursday to attend a summit of Asian and European leaders.

Ranariddh said the king’s decision was prompted by a letter he received from opposition leader Sam Rainsy, who complained that his party was being unfairly blamed for protests scheduled to coincide with the monarch’s return to Cambodia on Thursday.

But Sam Rainsy said his letter was not to blame.

“The king is … not a child. He cannot be influenced by anybody and be led that easily to make such a dramatic decision,” Rainsy said, calling Ranariddh’s allegation “irresponsible.”

The king in Cambodia is not a hereditary title, but all candidates must have a royal bloodline. Ranariddh could be a candidate, but has already said he is not interested.

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 months of political feuding.

The letter from the king asked the country to form a nine-member throne council _ as set in Cambodian law _ to choose the next monarch. Hun Sen and other political leaders would be included in the council.

A similar statement also appeared on Sihanouk’s Web site, where he often posts handwritten messages in French about current affairs. With that 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, as the future king.

The king asked that he be allowed to step down because of his fragile health, saying 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,” he said.

Chea Sim will remain the acting head of state until a new monarch is selected.

Lao Monghay, legal director for the Center for Social Development, a local group, said the king’s abdication was not surprising “considering his age and frustration over … the political developments in the country” and the lack of respect shown him by leaders.

“He seems to be sick and tired” of the political and economic situation facing the country, Lao Monghay said.