The State Department revealed Friday it has been quietly offering a $10 million reward to help track down the militants behind last year's deadly attack on a US mission in Libya. The brazen assault in Benghazi cost the lives of four Americans, including ambassador Chris Stevens, with the fatalities and disputes about what unfolded at the diplomatic base causing fury in Washington. A State Department spokesman told AFP that its Rewards for Justice program has since January been offering up to $10 million "for information leading to the arrest or conviction of anyone who was involved in the September 2012 Benghazi attacks."