Seoul: North Korea cannot return to six-way talks on its nuclear programmes unless the United States ends its financial crack down on Pyongyang's assets, Yonhap news agency quoted a senior North Korean official as saying.

The comments from Ri Gun, North Korea's deputy chief envoy to the talks, reiterated rather than hardened North Korea's stance but came as pressure builds for Pyongyang to return to the table.

North Korea has previously said it would be unthinkable to do so unless Washington ends its crack down on firms it suspects of aiding Pyongyang in illicit activities such as counterfeiting that it says help fund the North's nuclear programmes.

"As long as pressure continues, our position remains unchanged that we can't return to the six-party talks," Yonhap quoted Ri as saying.

A South Korean official in Seoul played down the remarks, which came after Ri met US Treasury officials on Tuesday.