Six-way working group nuclear talks ended in Beijing on Friday without a breakthrough in a 19-month standoff over North Korea's nuclear weapons program.

The talks snagged on stark differences between North Korea and the United States, the two protagonists in the dispute, but the six nations agreed to keep up the dialogue.

A South Korean delegate said the three days of discussions ended on a "wholesome" note, suggesting there was no breakdown.

North Korean negotiator Pak Myong-kuk told reporters that the six sides agreed to another round of working group discussions to pave the way for a third round of higher level six-party talks.

On Friday, North Korea and the United States held a bilateral meeting at which the U.S. pressed the North over an alleged uranium-based nuclear weapons program, quoting Pakistani nuclear scientist Abdul Qadeer Khan.

Pak denied the allegation that Khan had provided North Korea with highly enriched uranium technology, calling it "merely unrealistic and false information."

Pak told reporters outside the North Korean Embassy in Beijing that there had only been missile trade between Pyongyang and Karachi.

He said the U.S. claim is intended to create a mood of collective pressure on the North and that Pyongyang rejected the U.S. claim and made clear that they would never accept it.