Japanese chief negotiator to the fourth round of six-party talks on the Korean Peninsula nuclear issue Friday urged the Democratic Republic of Korea (DPRK) to review its stance on the issue of light-water reactor.

It was the key to "break the deadlock" of the talks, Kenichiro Sasae told reporters, adding that Friday is a "testing day" of the six-party talks.

He said that the Japanese side would "make utmost effort" to help reach an agreement at the talks, which was the common goal of all parites concerned.

All delegations to the six-party talks have been busily engaged in one-on-one and multilateral consultations over the past four days since the talks resumed Tuesday.

However, the negotiations failed to reach compromise on certain issues including the issue of light-water reactor.

"There are still great differences on certain issues," said Chinese delegation spokesman Liu Jianchao after a chief delegates' meeting on Thursday afternoon.

Earlier Friday morning, US chief negotiator told the media that it was hard to make a breakthrough over the issue of light-water reactor.

Source: Xinhua