"The U.S. should have taken steps towards lifting financial restrictions and discussed the issue with the Koreans," Alexander Losyukov said in an interview.
The talks, which involve North and South Korea, Russia, China, Japan, and the United States, were launched in 2003 to persuade Pyongyang to give up its nuclear ambitions.
In September 2005, North Korea signed a "joint statement" committing itself to abandoning its nuclear program in exchange for aid and security guarantees.
But the reclusive communist state boycotted the talks two months later following Washington's demand that its accounts at a Macau-based bank be frozen for alleged money laundering and counterfeiting of U.S. dollars. Since then, North Korea has conducted its first nuclear test and tested ballistic missiles.
The talks resumed last December following a 13-month standoff, but ended without result. At a symbolic ceremony, the six participant delegations made a joint statement reiterating their commitment to further negotiations in the same format.
Pyongyang said the future of talks depends on the position of the United States, and insisted that the possibility of scrapping its controversial nuclear program can only be discussed once financial sanctions are lifted.
Losyukov said Pyongyang should have been more flexible on the issue.
"The fact that North Korea is making this issue an obstacle for continuing the six-party process, aimed at resolving the nuclear problem, is also not 100% justified," he said.
"Both sides should contribute to progress," added said.
Losyukov, Moscow's former ambassador to Japan, appointed deputy foreign minister last week after his return from Tokyo, called on the negotiating parties to maintain close contacts to formulate a common position.
The diplomat was Russia's first envoy to the talks, and has now been reappointed, replacing Alexander Alexeyev.