Britons have been urged to leave Lebanon and avoid travel to the country as tensions soar in the Middle East.
Foreign Secretary David Lammy said events were “fast moving” and Foreign Office staff were working “round the clock” to help ensure the safety of UK citizens.
It came after Israeli Prime Minister Benjamin Netanyahu vowed heavy retaliation would follow a strike in the Israel-occupied Golan Heights which killed 12 children.
Mr Netanyahu blamed Lebanon’s Iran-backed Hezbollah group for the rocket, which struck a football field in Majdal Shams.
Unusually, Hezbollah has denied having any role in the attack.
Visiting the site of the attack, Mr Netanyahu said: “The state of Israel will not and cannot overlook this.
“Our response will come, and it will be severe.”
Around 300 mourners protested against Mr Netanyahu’s visit, accusing him of exploiting the bloodshed for political gain and calling for an end to the violence.
Early on Monday Israeli strikes hit a motorcycle in Lebanon near the border, killing two people and wounding three others, according to Lebanese state media.
Earlier in the day Israel’s defence minister Yoav Gallant also visited the town, warning Hezbollah would “pay a price” for the attack.
“We will let actions speak for themselves,” he said.
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Funeral for children killed in rocket strike
Rising fears of all-out war
Israel and Hezbollah have exchanged fire almost daily since the war between Israel and Hamas began in October, though the rhetoric following the latest strike raised fears the attacks could spiral into a full-fledged war.
Israel’s security cabinet has authorised Mr Netanyahu and Mr Gallant to decide on the manner and timing of the response to the strike.
People gather for the funeral of children who were killed at the football pitch in Majdal Shams. Pic: Reuters
The response would be “limited but significant,” Israel’s Yedioth Ahronoth newspaper quoted unidentified officials as saying.
The report said options ranged from a limited attack on infrastructure such as bridges, power plants and ports, to hitting Hezbollah arms depots or targeting the group’s commanders.
Mourners visit a makeshift memorial for 12 children killed in the strike. Pic: AP
‘Importance of preventing escalation’
US secretary of state Antony Blinken spoke to Israel’s President Isaac Herzog and emphasised the “importance of preventing escalation” and discussing efforts to reach a diplomatic solution to months of conflict.
Israel seized the Golan Heights from Syria after the 1967 war and has since annexed it, though the move is not generally recognised internationally.
Since October Israeli strikes have killed around 350 Hezbollah fighters in Lebanon and more than 100 civilians, according to a Reuters tally of Hezbollah death notifications.
Israel says 23 civilians and at least 17 soldiers have been killed in Hezbollah attacks since then.