UN peacekeepers in Lebanon warned Saturday against a "catastrophic" regional conflict as Israeli forces battled Hezbollah and Hamas militants on two fronts, on the holiest day of the Jewish calendar.

Israel has faced a fierce diplomatic backlash over the injuries suffered by five Blue Helmets serving in south Lebanon.

Lebanon's health ministry said Saturday that Israeli air strikes on three sites had killed at least 15 people, raising an earlier toll.

Israel observed Yom Kippur, the holiest day in the Jewish calendar, on Saturday amid a firestorm of international criticism over its military offensive in Lebanon and its soldiers firing on peacekeepers.

As the holy day got under way Friday from sundown, Israel faced diplomatic backlash over what it acknowledged was a "hit" earlier in the day on a United Nations peacekeeping position in Lebanon.

Two Sri Lankan peacekeepers were hurt in the second such incident in two days, the UNIFIL mission said Friday.

A US soldier who pleaded guilty to trying to provide information to the Islamic State group to help it attack American troops in the Middle East was sentenced to 14 years in prison on Friday.

Cole Bridges, 24, pleaded guilty in June of last year to attempting to provide material support to a designated foreign terrorist organization and attempting to murder US military service members.

Bridges, a private first class from Ohio, was sentenced to 14 years in prison on Friday and 10 years of supervised release, the Justice Department said in a statement.

Leaders from nine European countries around the Mediterranean Sea on Friday called at a summit in Cyprus for an end to fighting in Gaza and Lebanon.

French President Emmanuel Macron and Italian Prime Minister Giorgia Meloni condemned as "unacceptable" Israeli firing on UN peacekeepers in southern Lebanon, a stance echoed by Spain's prime minister.

The three countries together have around 2,000 troops in the UNIFIL mission, which said Israeli tank fire led to the injury of two of its peacekeepers on Thursday.

UN peacekeepers in Lebanon on Friday warned of "very serious risks" for their Blue Helmets after explosions wounded two mission members near the Israeli border, the second such incident in two days.

The Israeli military said its forces on Friday fired at a threat near a UN peacekeeping mission position.

Israel and Hezbollah have been clashing in south Lebanon since last week when Israel announced "targeted" incursions into Lebanon against the Lebanese militant group, which is backed by Iran.

Swedish activist Greta Thunberg attended a climate change and pro-Palestinian rally in Milan on Friday, days after her criticism of Israel sparked a row over protests in Germany.

More than 1,000 people, many of them teenagers, joined a peaceful march in the northern Italian city organised by Fridays For Future, the climate change movement Thunberg helped found.

Wearing a keffiyeh, a traditional scarf symbolising the Palestinian struggle against Israel, Thunberg walked near the front of the procession as other protesters waved flags, held banners and danced to music.

The displacement of hundreds of thousands of people in Lebanon is "devastating", a UN migration official has said, warning international support was falling short of the needs, amid intense Israeli bombing.

After a year of cross-border fire between Israel and Hezbollah, which launched attacks on Israel in support of its ally Hamas in Gaza, Israel last month escalated attacks on what it says are Hezbollah targets in Lebanon's south, east and south Beirut.

Lebanese Christian Joseph Jarjour was hoping for a peaceful retirement at home in south Lebanon, but has instead found himself caught in the crossfire of the Israel-Hezbollah war.

"We're trapped," said the 68-year-old retired teacher in the southern village of Rmeish, around two kilometres (one mile) from the Israeli border.

After almost a year of cross-border fire, Israel began conducting a wave of strikes targeting Hezbollah strongholds and sent ground troops across the border late last month.

Fearing becoming targets as the Middle East conflict spreads, wealthy Gulf states are shoring up ties with Iran and giving assurances they won't facilitate attacks by Israel, analysts said.

Traditionally Western allies, the resource-rich monarchies have grown closer to Iran after a long period of tension with their giant neighbour across the Gulf.

As Israel says it is preparing a response to Iran's 200-missile barrage on October 1, a rapid series of diplomatic exchanges shows the Gulf is keen to stress its neutrality in the conflict, experts said.

Israel observed Yom Kippur, the holiest day in the Jewish calendar, on Saturday amid a firestorm of international criticism over its military offensive in Lebanon and its soldiers firing on peacekeepers.

As the holy day got under way Friday from sundown, Israel faced diplomatic backlash over what it acknowledged was a "hit" earlier in the day on a United Nations peacekeeping position in Lebanon.

Two Sri Lankan peacekeepers were hurt in the second such incident in two days, the UNIFIL mission said Friday.