The United States, South Korea and Russia have urged North Korea to return to six-party talks on its nuclear ambitions by the end of this year.

The call was made Wednesday in Seoul following talks between U.S. Assistant Secretary of State James Kelly and his South Korean and Russian counterparts.

South Korean Deputy Foreign Minister Lee Soo-hyuck said new talks must take place this year, regardless of format.

The two Koreas, the United States, China, Japan and Russia have held three rounds of talks in Beijing on Pyongyang's nuclear ambitions, with little progress made.

A fourth round was scheduled for September, but North Korea refused to attend, saying the talks were worthless.