The United States said Monday that it had sanctioned a Chinese industrial machinery and equipment wholesaler, a new step in tightening the financial noose around North Korea's nuclear program after its fifth nuclear test this month.

The U.S. Treasury said it was sanctioning Dandong Hongxiang Industrial Development Co. (DHID) and four of its executives, including the firm's founder, Ma Xiaohong, under U.S. regulations targeting proliferators of weapons of mass destruction.

It accused the firm of acting on behalf of North Korea's Korea Kwangson Banking Corp. (KKBC), which has been under U.S. and U.N. sanctions for supporting proliferation of such weapons.