The attack was carried out on a guesthouse in a compound in Hasbaya being used by more than a dozen journalists from at least seven media organisations - with a courtyard containing cars clearly marked with "press".
The three men worked for broadcasters Al-Manar TV and Al Mayadeen TV, which issued statements paying tribute to their killed employees.
Lebanon's information minister said the attack was deliberate and described it as a "war crime".
The Israeli military has not yet commented, but has previously denied targeting journalists.
Those killed were camera operator Ghassan Najjar and engineer Mohamed Reda from pro-Iranian news channel Al Mayadeen, as well as camera operator Wissam Qassem from the Hezbollah-affiliated Al-Manar.
The Lebanese ministry of health said three others were injured in the blast.
Five reporters had been killed in prior Israeli strikes in Lebanon, including Reuters journalist Issam Abdallah.
Footage broadcast by Al-Jadeed TV - whose journalists were also sharing the house - showed a bombed-out building with a collapsed roof and floors covered in rubble.
A vehicle used for TV broadcasts was overturned on its side, its satellite dish mangled with cabling nearby.
"All official parties were told that this house was being used as a stay-house for journalists. We coordinated with them all," an Al-Jadeed journalist, caked in concrete dust, said in a live broadcast while panting and coughing.
Lebanese journalists covering the conflict in the south of the country had to relocate from nearby Marj'youn to Hasbaya, as the former became too dangerous.
Youmna Fawwaz, a reporter for broadcaster MTV Lebanon, told the BBC that journalists in the compound were awoken at around 03:00 local time (01:00 BST) by the strike.
She said ceilings had fallen in on them, and they were surrounded by rubble and dust, with the sound of fighter jets overhead.
Each news organisation had their own building in the compound, she said, and the building housing the Al Mayadeen reporters was "obliterated" while Al-Manar employees were inside.
Ms Fawwaz said it was a media compound known as such to both Israel and Hezbollah.
"The airstrike was carried out on purpose. Everyone knew we were there. All the cars were labelled as press and TV. There wasn't even a warning given to us."
She added: "They are trying to terrorise us just like they do in Gaza. Israelis are trying to prevent us from covering the story."
Lebanon's information minister accused Israel of intentionally targeting journalists, in contravention of international law.
"The Israeli enemy waited for the journalists' nighttime break to betray them in their sleep," Ziad Makary wrote in a post on X.
"This is an assassination, after monitoring and tracking, with prior planning and design, as there were 18 journalists there representing seven media institutions."
