Acting Assistant Secretary of State Susan Thornton told reporters in Beijing on Friday that China was increasingly aware of the urgency of pressuring North Korea to halt its testing of missiles and nuclear bombs.
She said Chinese officials say they've tightened border inspections, beefed up policing on the border and stepped up customs inspections.
China has announced a suspension of coal imports from North Korea through the rest of the year, but has been generally reticent about what other steps it's taking to use its leverage as Pyongyang's most important trading and diplomatic partner.