Humanitarian aid for North Korea has nearly ground to a halt this year as the United States steps up the enforcement of sanctions, despite warnings of a potential food crisis and improving relations with Pyongyang, aid groups say.

International sanctions imposed over North Korea's nuclear weapons programs technically do not cover humanitarian activities, and the United Nations recently adopted a U.S. proposal designed to streamline approval for aid shipments.

But strict interpretations of U.N. sanctions curtailing banking and shipping transactions with Pyongyang, as well as a travel ban for U.S. citizens, have effectively shut down the North Korea operations of most relief groups, according to a dozen officials at U.N. agencies and civilian organizations.