North Korean state media reported last month that drought in the west of the country suggests there will be food shortages this year.
A deal for food assistance from the United States collapsed in April when Pyongyang reneged on a pledge to halt nuclear and long-range missile tests.
Victoria Nuland, a spokeswoman for the U.S. State Department, said Washington was concerned but was forced to refer back to outstanding issues over North Korea's international obligations.
"We were … prepared to try to work on this issue until we became concerned about whether we could trust the word of the DPRK Government, and that's where we remain, unfortunately," she said during her regular press briefing.
Pyongyang has relied on foreign food assistance since the 1990s.
There were concerns expressed in April that Pyongyang might be ready to conduct a nuclear test. Missile launches in 2006 and 2009 coincided with tests of nuclear devices.
Washington in June extended a national emergency with respect to the nuclear threat posed by North Korea.
Beyonce flaunts bikini body, Blue Ivy in vacation pics
Gal Gadot cast as Wonder Woman for 'Batman vs. Superman'