Fuad Siniora said one million people – a quarter of the population – had been displaced by the fighting, which continued unabated on Thursday.
He made his remarks during a video statement sent to an Organisation of the Islamic Conference meeting in Malaysia on Thursday.
Lebanese security sources also said 80 Hezbollah fighters had been killed during the crisis, but Israel put the number at 300.
Israeli warplanes resumed their attacks on Lebanon on Thursday, a day after Hezbollah fired hundreds of rockets at Israel in its largest attack to date.
Meanwhile, about 10,000 Israeli troops were engaged in fierce clashes with Hezbollah fighters in five areas of southern Lebanon.
Israeli jets fired on the battered outskirts of Beirut as well as on the country’s northern border with Syria, the southern border with Israel and in the eastern Bekaa Valley.
Witnesses said at least four explosions reverberated through Beirut as missiles hit Dahieh, a suburb that has been repeatedly shelled by Israel.
It was the first air raid against the Lebanese capital’s southern suburb in almost a week.
The strikes came in the wake of Hezbollah’s rocket attack on the Israeli town of Afulah, its deepest hit in Israel so far.
Hezbollah said it fired more than 300 rockets into Israel on Wednesday, its largest assault to date, as fierce fighting raged on the border. Israeli officials said 210 had been launched.
Israeli jets also bombed roads and bridges near Lebanon’s northern border with Syria overnight, Lebanese radio said.
It was the second attack in the area in 24 hours, and a bridge linking the zone to the northern port of Tripoli was destroyed.
In the Bekaa Valley, some 75km to the south east of Beirut, witnesses said Israeli jets fired two missiles that hit a road.
An Israeli missile hit a house in the Lebanese border village of Taibeh killing a family of three, Lebanese security officials said.
One US-born Israeli was killed as he fled for a bomb shelter in Kibbutz Saar, a communal farm near the northern border town of Nahariya, on Wednesday.
Israel has a ground troop force of
Nineteen Israeli civilians have died during rocket attacks in the last three weeks.
One Israeli soldier was killed and four others wounded near the border village of Aita al-Shaab on Wednesday, the Israeli army confirmed early on Thursday.
The death brought to 37 the number of Israeli troops killed in 23 days of fighting.
56 Israelis have been killed in the conflict so far.
The US-based watchdog Human Rights Watch said that the bodies of 28 people killed in an Israeli air strike on the Lebanese village of Qana had been recovered and 13 people were missing.
An Israeli military inquiry into the attack on Qana admitted a mistake had been made, but said that Israel did not know that there were civilians in the building.