North Korean leader Kim Jong-il has failed to make a public appearance on a major annual holiday - fuelling fresh speculation about his health.
His absence from the Chuseok festival follows his failure last week to appear at a military parade on the 60th anniversary of his country's founding.
South Korean officials said he was recovering from a stroke - a claim Pyongyang dismissed as "worthless".
No-one has been named to succeed Mr Kim as leader of the nuclear-armed state.
The 66-year-old leader has ruled North Korea since the death of his father, Kim Il-sung, in 1994.
Six-nation negotiations aimed at making the secretive Communist state give up its nuclear weapons in exchange for much-needed aid and investment are currently at a standstill.
Mr Kim's absence from a triumphal military parade on Tuesday was followed by reports in the South Korean press, citing government officials, that the reclusive leader had received brain surgery after suffering a stroke.
WHO IS KIM JONG-IL?
N Korea's "Dear Leader" is a reclusive character, at the centre of an elaborate personality cult
Succeeded his father Kim Il-sung, founder of North Korea, who died in 1994
Mr Kim is seen in the West as both a master manipulator, and delusional madman
He has a reputation as a drinker, a playboy and a hypochondriac
"He's recovered enough to brush his teeth by himself," a Seoul official told the national news agency Yonhap last week.
However, other reports have suggested Mr Kim's recovery is slower than previously thought.
Japan's Mainichi Shimbun newspaper quoted a Chinese official on Sunday as saying that Mr Kim had been suffering seizures since April and was not fully fit to govern.
Meanwhile, North Korea's state-controlled media reported on Sunday that Mr Kim had been performing various official tasks - including sending birthday greetings to the Russian President Dmitry Medvedev.
Pyongyang officials have rebuffed reports that Mr Kim is unwell, dismissing them variously as "worthless" and a "conspiracy" by foreign media.
Mr Kim has not been seen in public since early last month. He has been known to disappear from public view for extended periods before, only to reappear later.
Concerns about Mr Kim's health come amid an impasse in international efforts to urge North Korea to abandon its nuclear programme.
North Korea agreed in February 2007 to give up its nuclear ambitions in return for aid and diplomatic concessions, but the progress of the deal has been far from smooth.
After a long delay, Pyongyang handed over details of its nuclear facilities in June 2008. In return, it expected the US to remove it from the list of state sponsors of terrorism.
But the two sides cannot agree on a process to verify the information that North Korea handed over and Pyongyang now appears to be starting to reassemble its main nuclear plant.
The North has relied on foreign assistance to help feed its 23 million people since its state-controlled economy collapsed in the mid-1990s
6 months ago