Three children and their grandmother have been killed in an Israeli airstrike targeting a car, according to a Lebanese official and local media.
Meanwhile, Gaza has fallen under its third total communications outage since the Israel-Hamas war began. The "new collapse in connectivity" across Gaza was reported by internet access advocacy group NetBlocks.org and confirmed by Palestinian telecom company Paltel.
In Lebanon, the state-owned National News Agency and Ali Safieddine, the head of the civil defence in the Tyre district, reported an Israeli strike targeted a car in southern Lebanon, between the villages of Aynata and Aitaroun.
One woman and three children, aged 10, 12 and 14, were killed and others were wounded, the news agency said, while a Hezbollah politician said the woman was their grandmother. Sky News has not been able to verify the report.
Hezbollah politician Hassan Fadlallah described the alleged attack as a "dangerous development", warning Israel would pay a price.
The militant group said it fired multiple grad rockets at the northern Israeli town of Kiryat Shmona in retaliation for the strike.
Lebanon will submit a complaint to the United Nations over the killings, the country's foreign minister Abdallah Bou Habib said.
Mr Bou Habib told Reuters that Lebanon was collecting information and pictures and would likely submit its complaint on Monday.
Israel's military also claimed on Sunday evening an Israeli was killed in an attack by Hezbollah.
It said its troops engaged a vehicle "identified as a suspected transport for terrorists" in Lebanon and it was looking into reports there were civilians inside.
Israel's forces have been exchanging with Iran-backed Hezbollah across the border in the north of the country since Hamas's attack on 7 October.
Other key developments:
• Scottish First Minister Humza Yousaf's parents-in-law have arrived in Scotland after fleeing Gaza;
• Israeli minister suspended after suggesting atomic bomb on Gaza is an option;
• Boris Johnson meets Israeli soldiers in Jerusalem to "express solidarity";
• Lebanon's ambassador to the UK claims Israel has used white phosphorus in southern Lebanon.
Meanwhile the communications outage in Gaza has made it even more complicated to share details on the latest stage of Israel's military offensive.
"We have lost communication with the vast majority of the UNRWA team members," UN Palestinian refugee agency spokesperson Juliette Touma told the Associated Press.
Palestinian telecoms company Paltel said: "The main routes that were previously reconnected [were] cut off again from the Israeli side."
The first outage in Gaza lasted 36 hours, while the second only lasted a few hours.
It comes as Israeli Prime Minister Benjamin Netanyahu repeated his warning that there will be no ceasefire until hostages held by Hamas are returned, as US Secretary of State Antony Blinken visited the West Bank on Sunday.
Mr Blinken later held a news conference in Baghdad in which he said he had a productive meeting with Iraqi Prime Minister Mohammed Shia' Al Sudani and also made "very clear" the attacks coming from militia aligned with Iran are "unacceptable".
"We had a good candid conversation and more broadly we are working hard to make sure the conflict in Gaza does not escalate to other places," he said.
Earlier in the day Mr Blinken met the Palestinian Authority president, Mahmoud Abbas, in the city of Ramallah on Sunday, as he continued his tour of the region.
Mr Abbas demanded an "immediate ceasefire" to allow humanitarian aid to the Gaza Strip, which Israel continues to bombard in response to Hamas's attack on Israeli civilians on 7 October.
"We demand that you stop them from committing these crimes immediately," Mr Abbas told Mr Blinken, according to a spokesperson.
Earlier on Sunday, Hamas, which has run Gaza independently of the Palestinian Authority since 2007, claimed an Israeli airstrike killed at least 47 people in the Maghazi refugee camp.
Violence has continued in the West Bank, with 121 Palestinians killed there since the war in Gaza began, according to UN figures.
Demonstrators call for ceasefire
Israel's siege of Gaza has also stirred global alarm at humanitarian conditions, with pro-Palestinian demonstrators protesting around the world on Saturday.
Demonstrations were held in cities including London, Berlin, Paris, Istanbul and Jakarta, with hundreds of thousands calling for a ceasefire.
There was also a protest in Washington to denounce President Joe Biden's war policy and demand a ceasefire.
The Hamas-run health ministry has said 21 Palestinians from the same family were killed in Israeli airstrikes on Gaza overnight.
It said in a post on its Facebook page that they belonged to the family of Abu Hasira and that the strike targeted a house that was "full of women and children".
Sky News has not independently verified the claim.