By Timour Azhari

BEIRUT (Reuters) -Israel said intense fighting erupted with Hezbollah in south Lebanon after its paratroops and commandos launched raids there, ahead of a widely expected ground incursion and after devastating airstrikes against Hezbollah's leadership.

The Israeli military said the operations in Lebanon began on Monday night and involved the elite 98th division, which was deployed to the northern front two weeks ago from Gaza where they had been fighting against Hamas for months.

It said its air force and artillery supported ground troops engaged in "limited, localised, and targeted ground raids" against Hezbollah in southern Lebanon villages that posed "an immediate threat to Israeli communities in northern Israel".

Israel has dealt heavy blows to Hezbollah, Iran's most powerful Middle East proxy, assassinating its leader Hassan Nasrallah in Beirut last week, eliminating a towering figure who turned it into Lebanon's top military and political force.

Despite its biggest successes against Hezbollah in decades, Israel has indicated it is primed for a full-fledged invasion of Lebanon with the stated aim of enabling thousands of its citizens who fled Hezbollah rockets to safely return to their communities near the northern border.

A Lebanese security source told Reuters that Israeli units had crossed into Lebanon overnight for reconnaissance and probing operations. Lebanese troops also pulled back from positions along the border, the source added. A Lebanese army spokesperson did not confirm or deny the movement.

Lebanon's army has historically stayed on the sidelines of major conflicts with Israel, and in the last year of hostilities has not fired on the Israeli military.

The operation into Lebanon represents an escalation of the conflict in the Middle East between Israel and Iran-backed militants that now threatens to suck in the U.S. and Iran.

Local residents in the Lebanese border town of Aita al-Shaab reported heavy shelling and the sound of helicopters and drones overhead. Flares were repeatedly launched over the Lebanese border town of Rmeish, lighting up the night sky.

Lebanon's armed group Hezbollah said on Tuesday it had targeted Israeli troops across the border in Metula twice with artillery and rocket fire but made no mention of Israel's launch of ground operations into Lebanon.

An Israeli strike in Lebanon early on Tuesday targeted Mounir Maqdah, commander of the Lebanese branch of the Palestinian Fatah movement's military wing, the Al-Aqsa Martyrs Brigade, according to two Palestinian security officials.

His fate was unknown.

The strike hit a building in the crowded Ain al-Hilweh Palestinian refugee camp near the southern city of Sidon, the sources said. It marked the first strike on Lebanon's largest Palestinian camp since cross-border hostilities between Hezbollah and Israel broke out nearly a year ago.

In Syria, three civilians were killed and nine others injured in an Israeli airstrike on the capital Damascus, Syrian state media said on Tuesday citing a military source. Israel's military said it does not comment on foreign media reports.

Israel has been carrying out strikes against Iran-linked targets in Syria for years but has ramped up raids since the Palestinian militant group Hamas attacked Israel's southern territory on Oct. 7, 2023.

Hamas killed 1,200 people and took about 250 hostage in its assault on Israel, according to Israeli tallies. Israel in response launched a massive assault on Hamas in Gaza, reducing most of the Palestinian territory to rubble, displacing most of its 2.3 million people and killing more than 41,300 Palestinians, according to the Gaza health ministry.

STRIKES ON BEIRUT

Israel's operations in Lebanon follows its deadly detonation of booby-trapped Hezbollah pagers, two weeks of airstrikes, and its killing on Friday of Nasrallah.

The intensive air strikes have eliminated several Hezbollah commanders but also killed about 1,000 civilians and forced one million to flee their homes, according to the Lebanese government.

Overnight, strikes hit Beirut's southern suburbs, a security source said. A Reuters reporter witnessed a flash of light and a series of loud blasts about an hour after the Israeli military warned residents to evacuate areas near buildings it said contained Hezbollah infrastructure south of the capital.

In the past 24 hours, at least 95 people had been killed and 172 wounded in Israeli strikes on Lebanon's southern regions, the eastern Bekaa Valley, and Beirut, Lebanon's health ministry said early on Tuesday.

Hezbollah's deputy leader Naim Qassem on Monday said "the resistance forces are ready for a ground engagement" adding that Hezbollah continued to fire rockets as deep as 150 km (93 miles) into Israeli territory.

The White House and the U.S. State Department did not immediately respond to a request for comment on Israel's ground operations in Lebanon, but on Monday, U.S. President Joe Biden had called for a ceasefire.

(Reporting by Cairo, Beirut and Washington newsrooms; Writing by Rosalba O'Brien and Michael Georgy; Editing by Himani Sarkar, Neil Fullick, Michael Perry and Miral Fahmy)