A senior U.S. senator has proposed a farm bill that includes a provision making any food aid to Pyongyang from Washington more difficult, congressional and diplomatic sources said Wednesday.

Senate Majority Leader Harry Reid (D-NV) re-introduced the five-year bill last month with the provision attached.

If passed in both chambers of Congress, it would prohibit the U.S. government from providing food assistance to North Korea without a presidential waiver.

Last year, the Senate passed the same version of the Farm Bill, but the House of Representatives did not take it up amid fierce partisan strife over ways to reduce the federal debt.

The congressional move to impose strict restrictions on food aid for North Korea came amid criticism that Washington often uses it as leverage for negotiations with the communist nation.

"The U.S. administration has made political decisions on food aid for North Korea. If the bill is passed, however, the process will become more tricky," a diplomatic source said.

The U.S. suspended the shipment of food to North Korea in 2009 after those who were monitoring distribution were banished.

Washington came close to resuming food aid in early 2012. But it scrapped the plan as Pyongyang fired a long-range rocket in April. (Yonhap News)