A prominent Lebanese activist known for his opposition to the Shiite movement Hezbollah was found dead in his car in the country's south on Thursday, a senior security official said.

Lokman Slim had not been heard from by his family since getting in his car on Wednesday evening to drive back to Beirut.

"He was found dead in his car, killed by a bullet to the head," the official said on condition of anonymity. Lebanese media also reported his death.

A journalist, political analyst and activist known as one of the leading Shiite voices criticising Hezbollah, Slim was regularly attacked in media loyal to the powerful group.

Security sources did not immediately elaborate on the circumstances of his death but Slim's own sister said before his death was even confirmed that his disappearance was inevitably linked to his opinions.

"He had a political stance, why else would he have been kidnapped," Rasha al-Ameer told AFP.

Slim was often criticised by Hezbollah supporters for being instrumentalised by the United States.

The secular intellectual and pro-democracy activist had also made several documentary films with his wife Monika Borgmann, who had sounded the alarm on social media when her husband went missing.

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