U.S. Secretary of State Rex Tillerson accused Russia on Wednesday of not implementing all United Nations sanctions on North Korea over its nuclear weapons program and said Moscow "may be frustrating" some of the steps.

Tillerson told reporters the Russian failure to comply with the U.N. measures "primarily" concerned fuel "but some other areas potentially as well." He did not provide details.

"It's apparent to us that they're not implementing all the sanctions and there's some evidence they may be frustrating some of the sanctions," Tillerson said aboard his aircraft while returning from a meeting on North Korea in Vancouver.