WASHINGTON -- Russia would be acting rationally if it sought to weaken the international sanctions regime against North Korea, a US expert on Korea said Tuesday.

Scott Snyder, chief Korea analyst at the Council on Foreign Relations, was commenting on concerns Russia has not been fully enforcing United Nations sanctions against Pyongyang. Russia, a veto-wielding permanent member of the UN Security Council, backed all four resolutions that were adopted last year in response to the North's nuclear and ballistic missile tests.

"Russian enforcement has been voiced as a concern at lower levels within the US government and now obviously it's reached to Trump," he said at a forum discussing North Korea sanctions.

US President Donald Trump said Monday that Russia has been "behaving badly" by "sending in what China is taking out."

Snyder acknowledged the concerns but noted that Russia is also under US sanctions for its occupation of Crimea and the violence in Ukraine.

"The Russians are being sanctioned by the US, while they're being asked to sanction North Korea, and I think that from the perspective of the Russian leadership it just makes no sense whatsoever," he said. "So frankly, it's a rational act for (Russian President Vladimir) Putin to seek opportunities to play a spoiler role in North Korea."

The US has led a "maximum pressure" campaign of increased economic and diplomatic sanctions to force North Korea to give up its nuclear weapons program. In the past few days, North Korea has expressed its openness to talks with the US, but the Trump administration has said it "will see" if the regime is serious and continue the campaign in the meantime.

Snyder also weighed in on South Korean President Moon Jae-in's analogy of Seoul being in the "driver's seat" on Korean Peninsula issues.

"For me, Moon in the driver's seat looks like a car that is going up a one-way mountainous road, perhaps with the US as the backseat driver blocking the rearview mirror, headed toward a burned out bridge -- destination Pyongyang on the other side," he said. "So the question is, you can't go forward, you've got to build the bridge if you're going to go forward or you've got to find a way to back down and reverse." (Yonhap)