WASHINGTON The United States and China will approve twice the number of passenger flights currently permitted for air carriers to fly between the two countries, sources and a document reviewed by Reuters show.

The U.S. Transportation Department will increase the number of Chinese passenger flights allowed to fly to the United States to 18 weekly round-trips on Sept. 1 and increase that to 24 per week starting Oct. 29 -- up from the current 12, and the Chinese government will agree to the same increase for American carriers, sources said. The agreement is a rare sign of cooperation between China and the United States that have clashed on many fronts.

(Reporting by David Shepardson)