Israel struck Hezbollah targets in southern Lebanon and the Iran-backed group attacked military facilities in northern Israel on Tuesday, increasing fears of a full-blown conflict after Lebanon suffered its deadliest day in decades.

Israel's military said it hit dozens of Hezbollah targets overnight, a day after carrying out airstrikes against the armed group that Lebanese authorities said killed over 550 people and sent tens of thousands fleeing for safety.

Hezbollah said it targeted several Israeli military targets overnight, including an explosives factory 60 kilometres into Israel, which it attacked with Fadi rockets around 4 a.m. local time. It said it had also attacked the Megiddo airfield near the northern Israeli town of Afula three separate times.

After almost a year of war against Hamas in Gaza on its southern border, Israel is shifting its focus to the northern frontier, where Hezbollah has been firing rockets into Israel in support of Hamas, which is also backed by Iran.

With the region increasingly on edge, over 30 international flights to and from Beirut on Tuesday were cancelled, according to the Rafic Hariri International Airport's website. Airlines affected included Qatar Airways, Turkish Airways and various airlines from the United Arab Emirates.

WATCH l Panic in Lebanon on the most violent day in decades: 

Israel intensifies airstrikes on Hezbollah in Lebanon

It’s being called the deadliest day of conflict in Lebanon in nearly 20 years. Israeli airstrikes on Hezbollah killed hundreds of people Monday, including children. The escalation has forced tens of thousands of people to flee in search of safety.

'Extremely alarming'

Some Lebanese hospitals are overwhelmed by the number of wounded, a World Health Organization official in Lebanon said, and Haifa's main hospital has moved operations to an underground facility after the Israeli city was attacked on Monday.

"We're looking at tens of thousands [of displaced in Lebanon], but we expect that those figures will start to rise," said the UN refugee agency's spokesperson, Matthew Saltmarsh. "The situation is extremely alarming."

The fighting has raised fears that the United States, Israel's close ally, and regional power Iran, which has proxies across the Middle East — Hezbollah, Yemen's Houthis and armed groups in Iraq — will be sucked into a wider war.

Maj.-Gen. Patrick Ryder, a Pentagon spokesperson, said a "small number of additional U.S. military personnel" will be sent to the region, where there are currently about 40,000 American troops stationed at various bases. The Pentagon declined to specify the precise number or mission of the deployed forces.

WATCH l UN, White House, Canada call for de-escalation on Israel-Lebanon front: 

Calls for de-escalation between Israel and Hezbollah grow as attacks intensify

Calls for immediate de-escalation between Israel and Hezbollah are growing louder after airstrikes killed hundreds in Lebanon on Monday. The U.S. is sending more troops to the Middle East, bolstering its presence in the region.

The strikes have piled pressure on Hezbollah, which last week suffered heavy losses when thousands of pagers and walkie-talkies used by its members exploded in the worst security breach in its history.

The operation was widely attributed to Israel, which has not confirmed or denied responsibility.

Israel's intelligence and technological prowess has given it a strong edge in both Lebanon and Gaza. It has tracked down and assassinated top Hezbollah commanders and Hamas leaders.

G7 concerned about regional war

Israel's military said about 55 projectiles had crossed into Israel in the latest attacks, but the majority were intercepted and several fallen projectiles had been identified in the Upper Galilee area.

"Damage was caused to buildings in the area," it said, adding that some of the projectiles were intercepted in the HaAmakim area and the rest fell in open areas.

WATCH l 'Wars have rules': Canada's UN ambassador Rae concerned about latest strikes: 

Canada 'deeply concerned' about Israeli airstrikes in Lebanon: Bob Rae | Power & Politics

Canada's Ambassador to the United Nations Bob Rae tells Power & Politics that the growing conflict between Israel and Hezbollah in southern Lebanon is a 'very disconcerting situation.'

Hezbollah said it had bombed the logistical warehouses of the 146th Division in the Naftali base with a rocket salvo.

Foreign ministers from the G7, including Canada's Mélanie Joly, said the Middle East risked being dragged into a broader conflict that no country would gain from, according to a joint statement released after they met on the sidelines of the UN General Assembly.

An all-out war could create instability across the Middle East in addition to a devastating war in Gaza, which shows no sign of easing.

Israel's potential options could include invading southern Lebanon and further broadening airstrikes to hit more of the Hezbollah-controlled southern suburbs of Beirut or Lebanese infrastructure, including bridges and highways that were blown up in the 2006 Israel-Hezbollah war.

Over 1,800 injured from Monday's strikes

Lebanon can ill afford such destruction as it is still suffering from a catastrophic financial collapse which its leaders have left to fester for five years.

Hezbollah would likely be a more formidable foe for Israel in a ground invasion than Hamas. Created in 1982 by Iran's Revolutionary Guards to counter the Israeli invasion of Lebanon, it has vast experience, is highly disciplined and possesses better weaponry than its Palestinian ally.

But Israel's government faces public pressure to secure its northern border and safely return residents there — a top war priority.

Families from south Lebanon on Monday loaded cars, vans and trucks with belongings and people young and old. Highways north were gridlocked.

Israel's military said it struck Hezbollah in Lebanon's south, east and north on Monday, including rocket launchers, command posts and militant infrastructure. The Israeli Air Force struck about 1,600 Hezbollah targets in southern Lebanon and the Bekaa Valley, it said.

Lebanon's health ministry said Tuesday at least 558 people had been killed in the previous day's strikes, including 50 children and 94 women, with 1,835 wounded.