The Biden administration offered up to $10 million as a reward for information on Salim Ayyash, a Hezbollah member sentenced in the killing of former Lebanese prime minister Rafik Hariri.
The US State Department announced the bounty on Monday through its Rewards for Justice programme, saying it is looking for the "senior operative in the assassination unit of the terrorist organisation Lebanese Hezbollah”.
The US designated Hezbollah as a foreign terrorist organisation in 1997.
The statement said the reward is also for information that could prevent Ayyash's involvement in terrorism against US targets.
“The reward offer is also for information that leads to preventing him from engaging in an act of international terrorism against US persons or US property,” the statement said.
His whereabouts are unknown. In 2020, the International Criminal Court sentenced him in absentia to five counts of life in prison over the assassination of Hariri.
The US government sees a continued role for Ayyash as "a senior operative in Hezbollah's Unit 121, the group's assassination squad", which it says receives its orders directly from the group's leader Hassan Nasrallah. It said that Ayyash is known to have been involved in efforts to harm US military personnel.
The US said Ayyash led the assassination team that carried out the attack and "was actively involved in the assassination on the day" of February 14, 2005.
David Re, the judge overseeing the Special Tribunal for Lebanon, said the court was confident in Ayyash's guilty verdict.
"Mr Ayyash intended to kill Mr Hariri and had the required knowledge about the circumstances of the assassination mission, including that explosives were the means to be used,” the judge said before the sentencing last December.
He remains at large and Hezbollah has denied accusations about its role in the assassination.
The reward comes only a few days after US military linguist, Mariam Taha Thompson, pleaded guilty to leaking secrets to Hezbollah through a lover – a man she never met – while in Iraq. She faces life in prison.