The U.S. envoy to the United Nations accused Russia of “actively working to undermine” international sanctions against North Korea as pressure rises on the Trump administration three months after the president met Kim Jong Un in Singapore, Bloomberg reported.

“Why after voting for sanctions 11 different times is Russia backing away from them? We know the answer. Its because Russia has been cheating. And now they’ve been caught,” Ambassador Nikki Haley said Monday in an emergency session of the Security Council she called late last week.

The U.S. says its effort to keep pressure on North Korea’s economy through sanctions approved by the Security Council is being undermined by Russia, who the Americans accuse of helping Kim’s regime skirt the restrictions.