WASHINGTON, USA (AFP) — The US State Department disclosed yesterday it is offering a $10-million reward to track down anyone behind last year’s brutal attack on a US mission in Libya, in which the ambassador was among four Americans killed.

“Since January of this year, the Rewards for Justice programme has had a reward offer of up to $10 million for information leading to the arrest or conviction of anyone who was involved in the September 2012 Benghazi attacks,” a State Department spokesman told AFP on Friday.

The reward was not widely publicised when it was first made available, which the State Department said was because of “security issues and sensitivities surrounding the investigation”.

“Since this event happened… we’ve made it clear that we are committed to bringing the people who conducted this attack to justice. And we’re using all the appropriate tools we have to do that,” the spokesman said.

Hordes of heavily armed militants stormed the mission in eastern Benghazi on September 11, 2012 and then attacked a nearby CIA compound with mortar shells and rockets.

Ambassador Chris Stevens was killed in the firestorm along with three other diplomatic and security staff, Sean Smith, Glen Doherty and Tyrone Woods.

Stevens, a popular diplomat and fluent Arabic speaker, was the first ambassador to be killed while on duty in three decades, and the assault shocked America to its core.