Since 2006, Yemen’s military has received some $400 million in US Defense Department train-and-equip aid, according to the US Congressional Research Service. Additionally, the US State Department provided aid to Yemen in the amount of $356 million in 2012, $256 million in 2013 and $142 million in 2014.
"With not having the ability to be in Yemen currently to monitor the disposition of weapons then we don’t have the ability to oversee the safeguarding or deployment of those weapons systems,” Austin said at a US Senate Armed Services Committee.
Austin said "it is reasonable to suspect" the US-provided weapons would fall into the hands of groups in Yemen opposed to the United States.
On Wednesday, Yemen's Houthi rebels gained further ground as they approached the city of Aden. Following their advance and calls from President Abd Rabbuh Mansur Hadi for intervention, a Saudi Arabia-led coalition of Arab nations started carrying out airstrikes against Houthi positions.
While not participating in the offensive, the United States is backing its Arab allies and has agreed to provide logistical and intelligence support for the military operation.
The coalition's airstrikes triggered a wave of protests in Sanaa, with thousands of people taking to the streets.
Aid by the United States to the Yemeni military for operations against al-Qaeda was described by US President Barack Obama in September 2014 as a successful example of US counter-terrorism efforts.
