The U.N. Security Council agreed Monday to a Chinese request to remove sanctions on four ships the United Nations had blacklisted for ties to Pyongyang's arms trade. The agreement came after China secured assurances the vessels will not use North Korean crews, a U.S. official said.

China asked the United States last Wednesday for help removing the ships from the U.N. blacklist, according to a diplomatic cable sent the same day from the U.S. Mission at the United Nations to a group of other U.S. embassies.

The contents of the cable, seen by Reuters, showed wrangling between top diplomats from the United States and China over the tough new North Korea sanctions, weeks after Washington had presented a united front with Beijing, Pyongyang's main ally and trade partner.