"We will not participate in the Moscow talks," he said, adding that the US supports the process itself and may join a similar meeting in the future.
"It's just logistically difficult for us to take part this week to support the process," he said, TASS reported.
He also noted that the Troika plus format (Russia, the US, China, Pakistan) is an "effective and constructive forum."
"We look forward to engaging in that forum, going forward, but we're not in a position to take part this week," he added.