A prominent Lebanese Shi'ite critic of Iran-backed Hezbollah was found dead in a car in southern Lebanon on Thursday, two security sources and local media said.
The sources said Lokman Slim, an activist and publisher who ran a research centre, was shot with a bullet to the head.
They said the motive was not immediately clear and a preliminary investigation was underway.
One of the security sources said Slim's phone was found earlier on the side of a road in southern Lebanon, where Shi'ite Hezbollah has a dominant presence. It was the first such alleged killing of a leading anti-Hezbollah activist in years.
Slim's family said he went missing overnight. His wife tweeted that he was not answering his phone.
A relative said the family found out about his death from a news alert while at a police station to report his disappearance.
At the family home in the southern suburbs of Beirut, family members sat in silence and shock, while some wept.
Slim's criticism of Hezbollah has faced rebuke from supporters of the armed movement, who sometimes called him "an embassy Shi'ite," a term accusing opponents of being tools of the United States.
Washington deems Hezbollah a terrorist organization and has ramped up sanctions against its officials and allies in Lebanon in recent years.
Hezbollah did not immediately respond to a request for comment.
