WASHINGTON, March 21 (Reuters) - The United States imposed sanctions on Thursday on two Chinese shipping companies it says helped North Korea evade sanctions over its nuclear weapons program, the first such steps since a U.S.-North Korean summit collapsed last month.

The U.S. Treasury Department also issued an updated advisory that listed 67 vessels that it said had engaged in illicit transfers of refined petroleum with North Korean tankers or were believed to have exported North Korean coal.

The department identified the newly sanctioned firms as Dalian Haibo International Freight Co Ltd and Liaoning Danxing International Forwarding Co Ltd, which it said had helped North Korea evade U.S. and international sanctions.