The Obama administration has offered up to $10 million since January for information on those who attacked the US consulate in the Libyan city of Benghazi, the State Department said Friday.
The disclosure about the offer made under the agency's "Rewards for Justice" programme and was unveiled in a letter sent to members of Congress, reported Xinhua.
Some lawmakers had complained that the department was not using all possible means to deliver on promises by President Barack Obama to bring the perpetrators to justice.
The attack Sep 11, 2012, in which US Ambassador Christopher Stevens and three Americans were killed, still haunts the Obama administration, as the Republicans have been pressing for truth about the attack.
The White House offered conflicting accounts of the raid, initially as one triggered by anti-American demonstrations and later as an act of terrorism by militants with links to al-Qaida.
No arrests have been made as separate investigations by the Federal Bureau of Investigation and the Libyan authorities are still under way.
