King Bhumibol Adulyadej was scheduled to take part in a birthday ceremony at the Grand Palace's throne hall but it was canceled due to an illness that also prevented him from delivering his annual birthday speech Thursday, local media said.

Many Thais had been eagerly awaiting his address in hopes it might point a way out of political turbulence that in the past two weeks has included a seven-day seizure of Bangkok's two airports by anti-government protesters and the ouster of the government, backed by the rural poor. The capital's Suvarnabhumi International Airport officially reopened Friday, but was operating at only about 50 percent capacity.

Early Friday, hundreds of Thais gathered on a field outside the ornate, walled palace to give alms to 282 Buddhist monks as a way of conveying their best wishes to the king.

"The conflict between the groups will linger on and hurt the country's economy and reputation for years," said Jiraporn Chaoprayoon Yamamoto, a social worker.

"I think with his majesty the king's weak health condition and the political conflict that divides Thais in two, Thailand's future is bleak," she said. Like many Thais, she said she was praying for the king's recovery.

On Thursday, Princess Sirindhorn said the king was weak and suffering from bronchitis and inflammation of the esophagus but that his "condition is not serious."

The king's last public appearance was Tuesday when he looked haggard while inspecting royal troops. He spoke briefly, reading hoarsely from a text, and seemed barely able to keep his head up.

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.

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

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.

It started with mass protests in late 2005 to oust then Prime Minister Thaksin Shinawatra, who was removed in a 2006 military coup amid accusations of gross corruption and attempting to undermine the monarchy. The coup is widely believed to have been backed by the palace.

Thaksin's supporters won elections held in December 2007. But the protest alliance rejected the outcome, saying the new government was a proxy for Thaksin, and began another round of agitation that culminated with the seizure of Bangkok's two airports.

The alliance - backed largely by the urban middle class - ended its airport siege after a court Tuesday ousted the government for voter fraud in the last elections.