Vietnam's foreign minister has pledged to try to resolve by the end of the year 70 cases of missing U.S. servicemen that the United States considers of highest priority, Voice of Vietnam said Thursday. Minister Nguyen Co Thach was quoted as saying he welcomed U.S. participation in joint excavations for the remains of missing servicemen. The United States is trying to account for nearly 1,800 Americans missing in action from the Vietnam war, which ended in April 1975 with a communist victory over the U.S.-backed South Vietnamese government. The broadcast said Thach wrote July 9 to retired Gen. John W. Vessey, a special presidential envoy, in which he urged the United States to "carry out all agreements relating to humanitarian issues relating to Vietnam."