He has not been seen in public for several weeks, with speculation growing that he may have suffered a stroke, or may possibly already be dead, casting doubt over who is making key decisions about the country's nuclear programme.
"We all know what we're supposed to get accomplished here and, like all these six-party meetings, it will be difficult negotiations"
chief US envoy to talks
Under the original six-nation pact agreed in early 2007, Pyongyang agreed to disable facilities at its plutonium-producing Yongbyon nuclear complex and reveal its atomic activities.
In return, it was to get one million tonnes of fuel oil or energy aid of equivalent value.
But the deal became bogged down by a series of disputes and so far only about half the promised aid has been delivered.
In October this year, after an apparent agreement on procedures to verify the North's disarmament, the US said it would drop North Korea from its list of state sponsors of terrorism.
At the same time the North reversed plans to restart its plutonium-producing nuclear reactor.
Now though a new hurdle has been thrown up with North Korea opposing the idea of atomic samples being taken out of the country for testing by inspectors.
The US says this is a key part of the process of verification.
|US envoy Christopher Hill is under pressure to secure a deal before Bush leaves office [AFP]
"After hearing what was discussed between the US and North Korea [in Singapore last week], it appears a big gap still remains, Akitaka Saiki, the Japanese nuclear envoy, told the Associated Press.
"Regarding how to narrow the gap, it's up to each party's efforts from tomorrow. I think negotiations are going to be tough.''
Progress may be further hampered by the North's decision to ignore Japan's presence at the talks.
Tokyo has withheld its share of fuel aid to the North until it fully accounts for Japanese nationals kidnapped by North Korean agents during the Cold War.
The North has admitted it seized Japanese civilians to train its spies, and in 2002 let five of them return home. It insists the others are dead, but Japan believes they are alive and still being held in North Korea.
The latest round of talks are likely to be the last before Bush leaves office, and analysts have said North Korea is unlikely to make any serious decisions before Barack Obama, the US president-elect, takes office in January.
Chung In-moon, a political scientist at Seoul University, told Al Jazeera that he believed Christopher Hill, the US nuclear envoy, will have a difficult time at the talks.
"The Bush administration is leaving office soon, so Hill will be under pressure to provide a good result," he said.
Speaking ahead of Monday's meeting Hill himself said he was prepared for some tough negotiations.
"We're not trying to solve all the problems, but we have several items that we have worked hard to get ready, Hill told the Reuters news agency.
"We all know what we're supposed to get accomplished here and, like all these six-party meetings, it will be difficult negotiations."