Talks on North Korea's nuclear programme face problems due to Pyongyang's "excessive" energy demands, a Japanese delegate has said.
Mr Sasae said North Korean demands were "excessive"
Six-nation talks on the nuclear programme are entering a fourth day in the Chinese capital Beijing.
At stake is a draft agreement under which Pyongyang would reportedly close nuclear facilities in exchange for aid.
Chief US negotiator Christopher Hill was hopeful for a resolution, but the South Koreans and Japanese have doubts.
"We are down to one main issue which I think we can get through" said Mr Hill. "It may take another day or two."
But Japan's chief negotiator Kenchiro Sasae, expressed doubts over a deal.
"The gulf between North Korea and us is considerably large, and whether we can fill in the gap solely depends on North Korea," he said.
"Although we are going to have discussions today, we are not in a situation where we can be optimistic ... With respect to energy aid, the problem is North Korea has excessive expectations. Unless North Korea changes their expectations, it will be difficult to reach an agreement."
South Korean delegate Chun Yung-woo said the barrier was not the amount of oil the North was seeking, but how aid was "tied to the scope and speed of the actions of denuclearisation" to be taken by the North.
"It's a bit unreasonable to expect there'll be a breakthrough today," he said.
'Twists and turns'
"The discussion focused on what the five countries would do in the process of North Korean denuclearisation," Mr Sasae said after Saturday's discussions.
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"There are differences of opinion among the five nations, but there are greater differences between the five nations and North Korea," the envoy added.
Chinese Foreign Ministry spokesman Qin Gang agreed that "fairly big differences" still existed between the parties.
"We do expect to see good progress although we are still likely to face twists and turns," Mr Qin was quoted as saying by the Associated Press.
Chinese officials drafted their outline plan after Pyongyang agreed to take initial steps towards disarmament.
The one-page plan reportedly involves calls for the shutting down of Pyongyang's plutonium-producing reactor at Yongbyon within two months and the return of international inspectors, in exchange for deliveries of fuel oil.
The US and South Korea would provide oil and other aid within the same time-frame.
The BBC's James Reynolds, in Beijing, says the fact the six parties are considering a draft agreement will be seen by many as a step forward.
It is certainly a change from the last round of talks held in December, in which no progress was made at all, our correspondent says.