WASHINGTON - US Secretary of State Rex Tillerson and Chinese State Councilor Yang Jiechi discussed improving and maintaining a 'mutually beneficial economic relationship' between the United States and China, the State Department said on Tuesday. Tillerson and Yang, China's top diplomat, also affirmed the importance of 'regular high-level engagement' between the two countries during their meeting in Washington, and discussed North Korea's nuclear program, the State Department said in a statement. Yang's visit to the United States follows a phone call between him and Tillerson last week, during which the two affirmed the importance of a constructive US-China relationship.