Israel ordered residents of a vast region of southern Lebanon to leave their homes on Wednesday, as Lebanese authorities announced at least 72 people killed since Monday, 437 wounded and 83,000 displaced from their homes.

Hezbollah, whose leader Naim Qassem is scheduled to speak at 1900 GMT, stepped up its attacks against Israel on Wednesday, saying it targeted Israeli positions as far as Tel Aviv, in at least 15 attacks.

Lebanon was drawn into the Middle East war on Monday when the Iran-backed militant group Hezbollah attacked Israel in response to the killing of Iranian supreme leader Ayatollah Ali Khamenei during US-Israeli strikes over the weekend.

The Israeli military told people living south of Lebanon's Litani river -- around 30 kilometres (20 miles) north of the border -- to evacuate, warning that the army was "compelled to take military action" against Hezbollah in the area.

On Tuesday, Israel's military said it was creating a buffer zone inside Lebanon to protect Israeli residents.

Israeli troops from three divisions, including infantry, armoured and engineering units were operating inside southern Lebanon, Israel's army said late Wednesday.

AFP video footage shot on Wednesday showed what appeared to be two Israeli tanks amid residential buildings in Khiam, about six kilometres north of the border.

"Peacekeepers observed today several IDF (military) movements and military activities, including near... Khiam, Beit Lif, Yaroun, Houla, Kfar Kila, Kherbeh and Kfar Shouba," the UN peacekeeping mission, UNIFIL, said in a statement.

It added that the Israeli movements violate Lebanon's "sovereignty and territorial integrity".

Israel announced Wednesday two of its soldiers had been "moderately injured" by anti-tank fire while "operating in southern Lebanon".

Hezbollah said its fighters have engaged Israeli troops in "direct" clashes in Khiam, "inflicting confirmed casualties".

- Hotel strike -

Meanwhile, Israel expanded the scope of its aerial campaign, striking a hotel in Hazmieh, the first reported Israeli attack on the predominantly Christian area in Beirut's suburbs, near the presidential palace and several foreign embassies.

Some rooms were gutted in the strike, while wounded people received treatment in the lobby, AFP images showed.

People fled through debris carrying suitcases past the Comfort Hotel's sign, which had fallen broken to the ground. It was not possible to determine who was targeted in the attack.

The upscale district overlooks the capital's southern suburbs, which Hazmieh resident Lena had initially thought was the target of the strikes.

"I was wrong," the 59-year-old woman told AFP. "Just a stone's throw from my home, a hotel was targeted."

Several people told AFP they had received recorded phone messages telling them to evacuate, a security official told AFP.

- Southern suburbs targeted -

A series of strikes on Wednesday continued to target Beirut's southern suburbs, where Hezbollah holds sway, following an evacuation order from Israel's military.

One of the strikes targeted a building near a major hospital, according to an AFP photographer.

AFP footage showed thick plumes of smoke rising above buildings in the densely populated suburb, where some residents fled when the violence erupted on Monday.

In Aramoun and Saadiyat south of Beirut -- two towns outside of Hezbollah's traditional sphere of influence -- the health ministry said Israeli strikes killed six people and wounded eight others. It cautioned that this was a "preliminary toll".

AFP footage from Aramoun showed damaged cars and rescue workers carrying a wounded person on a stretcher.

Strikes also targeted a four-storey building in the city of Baalbek, in Lebanon's east, far from the border where Hezbollah also has a strong presence.

AFP correspondents saw rescue workers searching through the rubble for survivors.

Israel continued to strike a number of other areas including Tyre, Nabatieh, and other locations in the Baalbek district on Wednesday.