More than 220 people also wounded, several of those when security forces opened fire at a group in Al Nour Square.
A prominent Lebanese activist known for his opposition to Hezbollah has been found dead in his car in the country’s south, security officials and local media 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,” an official told the AFP news agency on Thursday on condition of anonymity.
A security source told Al Jazeera an investigation is under way, and it appeared Slim was shot twice in the head.
State news agency reported that Slim’s body was taken to the Saida Government Hospital and that a medical examination revealed that he was shot four times in the head and once in the back.
Slim’s sister said before his death was even confirmed 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, one of the most prominent Lebanese intellectuals to be gunned down since historian Samir Kassir in 2005, was born in Beirut in 1962 and studied in France towards the end of the 1975-1990 civil war.
A journalist, political analyst and activist known as one of the leading Shia voices criticising Hezbollah, Slim was regularly attacked in media loyal to the powerful group.
Slim was often criticised by Hezbollah supporters for being instrumentalised by the United States.
Slim co-founded Umam Documentation and Research in 2005, a non-profit that most notably included an extensive historical archive and a cultural and exhibition space, and civic organisation Hayya Binna (Let’s Go).
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.
Hezbollah condemned the killing of Slim in a statement late on Thursday.
“We ask the judicial and security authorities concerned to work quickly to expose the culprits and punish them,” the group said.
Al Jazeera’s Zeina Khodr, reporting from Beirut, said Hezbollah has denied the group’s involvement in the killing and say the accusations are politically motivated.
“But many people point out the fact of who [Slim] was; he was a Shia, from the same sect of Hezbollah and he used to live among them in their heartland, which for many was a thorn in the side of the group,” she said.
“[In] Lebanon at the moment, dissent is growing, calls for new leadership is growing, and calls for early elections. So there’s condemnation, there’s anger, and there’s grief, but there’s also fear, with activists telling us that media freedoms and freedom of expression is at risk … they are seeing the killings as a message to silence dissent.”
Interior minister Mohammed Fahmi, quoted in local media, called Slim’s killing a “horrible crime”.
Lebanon’s President Michel Aoun called on the public prosecution to carry out a swift investigation into the murder.
The Future Movement, led by Prime Minister Saad Hariri, condemned the assassination. “We warn of the risks of returning to a series of assassinations and targeting activists,” it said in a statement.
Bassem Sabeh, a former Shia member of Parliament and a critic of Hezbollah, said Slim’s assassination was a “direct messages to all activists, writers and politicians from the Shia community, who mobilise and express their ideas outside of Hezbollah’s political orbit”.
Veteran journalist Diana Moukalled said Slim’s apparent assassination was the consequence of his outspokenness and Slim had been subject to “direct threats” and smear campaigns by Hezbollah-affiliated and allied media in recent years.
“He was very strong in his convictions, and was his work was electric, not just about Hezbollah,” Moukalled told Al Jazeera, referring to his work on culture and human rights issues with Umam.
“He is a huge loss for the country.”
Kareem Chehayeb contributed to this report from Beirut, Lebanon.