The U.S. Defense Department cannot account for more than $500 million in U.S. military aid to Yemen, and officials are worried that small arms, ammunition, patrol boats, vehicles, and other equipment might end up in the hands of al-Qaeda or Iranian-backed rebels.

#Business The US reportedly lost track of A LOT of military equipment in Yemen http://t.co/9eWxxUdflI pic.twitter.com/gMnhdou7lJ — Matteo Vismara  (@wizardxp) March 17, 2015

In January, Yemen's government was toppled by Houthi rebels, who have also taken over several military bases in the northern part of the country that were home to U.S.-trained counterterrorism units, The Washington Post reports, and it became even harder to keep track of things in the country once the U.S. embassy closed in February.

A defense official speaking on the condition of anonymity told the Post there's no evidence the arms or equipment are in the wrong hands, but did confirm that the Pentagon has lost track of the items. The U.S. government had limited its lethal aid to small firearms and ammunition, ignoring requests from Yemen for fighter jets and tanks, and stopped $125 million worth of shipments to Yemen that were scheduled for delivery this year, the defense official said; drones, Jeeps, and aircraft were instead donated to countries in Africa and the Middle East. Catherine Garcia