U.S. President Donald Trump on Monday referred to a vague joint statement agreed to at his landmark summit with North Korean leader Kim Jong Un in Singapore last month as a "contract," saying he believed Kim would "honor" the agreement while also pointing a finger at China for "exerting negative pressure."

"I have confidence that Kim Jong Un will honor the contract we signed &, even more importantly, our handshake," the Trump wrote on Twitter. "We agreed to the denuclearization of North Korea. China, on the other hand, may be exerting negative pressure on a deal because of our posture on Chinese Trade-Hope Not!"

However, at the Singapore summit, North Korea did not specifically itself agree to denuclearize. Rather, the document that Kim and Trump signed said that Pyongyang was committed to "work towards the complete denuclearization of the Korean Peninsula" — language that some observers say gives it room to maneuver for a phased, quid pro quo approach with the U.S.