New Delhi, Jan. 30 -- The United Nations food agency is shutting down its operations in the northern, rebel-held part of Yemen, following restrictions imposed by the Houthi rebels and harassment from the Iranian-backed group, U.N. officials said Thursday.

The World Food Program's move is likely to worsen the dire humanitarian conditions in the impoverished Arab country amid the rebel Houthis' crackdown on U.N. workers and aid groups in areas under their control, as well as funding shortages.

Yemen descended into a devastating civil war in 2014, when the Houthis pushed from their northern stronghold of Saada province and seized the capital of Sanaa, forcing the internationally recognized government out and to the south, and eventually in...