Diplomatic pressure mounted Monday to avert an escalation between Iran and Israel following high-profile killings that have sent regional tensions soaring.

Israeli Prime Minister Benjamin Netanyahu said late Sunday that his country was "determined to stand against" Iran and its allied armed groups "on all fronts".

As its war against Iran-backed Hamas in Gaza nears the 11th month, Israel has been bracing for retaliation from the Tehran-aligned "Axis of Resistance" for the killing of two senior figures.

Once a day, Umm Omar picks up the phone and calls her late husband, humouring their four-year-old daughter who does not understand yet her father was killed early in the Gaza war.

Little Ella "wants us to call him, to tell him about her day", said Umm Omar, who has fled with her three children to Al-Mawasi, a coastal area teeming with mostly displaced Palestinians in the southern Gaza Strip.

Travellers waited in long lines at Beirut airport on Sunday, some after cutting summer holidays short, as airlines have cancelled flights and fears have grown of all-out war between Israel and Hezbollah.

"I'm not happy to leave. I wanted to spend the whole summer in Lebanon then go back to work" in France, said Joelle Sfeir from the crowded departures hall at Beirut airport.

But "my flight was cancelled and I was forced to book another ticket today," she told AFP.

"I cut my trip short so I could find a flight," she added.

Gaza's civil defence agency said an Israeli strike hit two schools in Gaza City on Sunday, killing at least 30 people, while the military reported it had struck Hamas command centres.

These bring to at least 11 the number of schools in Gaza to be struck since July 6, killing around 150 people, based on a tally of tolls previously given by officials in the Hamas-run territory.

"The number of martyrs in the massacre of the Hassan Salameh and Al-Nasr schools' bombing has risen to 30. Dozens were also wounded," civil defence spokesman Mahmud Bassal told AFP.

Algerian teenager Kaylia Nemour conjured up "the performance of her life" to become the first African to win an Olympic gymnastics medal with gold on the uneven bars on Sunday.

The 17-year-old French-born athlete took the title ahead of China's Qiu Qiyuan, who took the world title ahead of the Algerian last year, with American Sunisa Lee snatching bronze.

Defending champion Nina Derwael of Belgium finished fourth.

"I'm so shocked, it's the dream of all my life. I can't believe it has happened, I'm the Olympic champion. I'm speechless," said Nemour.

When Israeli air strikes hit his neighbourhood early on in the Gaza war, Palestinian social worker Tareq Abu Eita, 42, saw his whole life upended in seconds.

The bombardment on October 14 blew in the walls of his two-storey family home.

It killed his 77-year-old father Hamed, his wife of 15 years Muntaha, 37, and his 11-year-old son Ilyas.

It also took the lives of his two nieces, eight-year-old Mira and 14-year-old Tala.

Jordan's Foreign Minister Ayman Safadi held talks Sunday during a rare visit to Iran, as fears of an escalation between Tehran and Israel grew following the killing of Hamas chief Ismail Haniyeh.

The political head of Palestinian militant group Hamas was killed early on Wednesday in Tehran, where he had attended the inauguration of Iran's President Masoud Pezeshkian.

Iran and the Hamas militants, which Tehran supports, vowed to retaliate and blamed the strike on Israel, which has declined to comment.

Urgent calls grew for foreign nationals to leave Lebanon, which would be on the front line of a regional war, as Iran and its allies readied their response to high-profile killings blamed on Israel.

While diplomats worked to avert a feared conflagration, France's Emmanuel Macron and Jordan's King Abdullah II said Sunday a regional military escalation must be avoided "at all costs", the French presidency said after they held a telephone call.

Urgent calls for foreign nationals to leave Lebanon grew on Sunday with France warning of "a highly volatile" situation as Iran and its allies ready their response to high-profile killings blamed on Israel.

Lebanon's Iran-backed Hezbollah movement, which has traded near-daily fire with Israeli forces since the Gaza war broke out in October, announced its fighters had fired a barrage of rockets at Israel's north overnight.

The Israeli military said 30 projectiles were launched from Lebanon, with most of them intercepted.

Hundreds gathered near Beirut's port on Sunday to mark four years since a catastrophic explosion devastated the capital and to demand accountability, with the spectre of war weighing over commemorations.

Nobody has been held responsible for the August 4, 2020 blast -- one of history's biggest non-nuclear explosions -- which killed more than 220 people, injured at least 6,500 and devastated swathes of the capital.