A number of suburbs in the Hezbollah stronghold were struck, with local TV showing fires in the night sky.

The Israeli defence minister has told the army to prepare for a push to the Litani river, up to 30km (19 miles) north of the border, officials said.

The moves came as UN delegates in the US struggled to reach full agreement on the wording of a ceasefire resolution.

Israel's campaign began three weeks ago after Hezbollah militants captured two Israeli soldiers.

Lebanon says more than 900 people have died since then, most of them civilians. Israel has lost 27 civilians and 40 soldiers.

'Sign of weakness'

Israel had dropped leaflets on Thursday in the Lebanese capital saying: "After the continued launching of Hezbollah terrorist rockets... the IDF [Israeli Defence Forces] intend to widen their offensive in Beirut."

Early on Friday, local media reported strikes on the Ouzai neighbourhood of southern Beirut.

The media also said Israeli warships had shelled the suburbs of Haret Hreik and Roweiss.

The Israeli military told Reuters news agency it had targeted Hezbollah offices and the home of a top Hezbollah official, along with a building operated by Palestinian group Hamas.

Israeli jets also struck three bridges north of Beirut, killing at least one person.

The attacks came as Israel's army was ordered to prepare for what could be its deepest push into Lebanon for more than 20 years.

Three Israeli soldiers have been killed in southern Lebanon, according to Arabic TV channel al-Arabiya.

The air strikes occurred despite a warning from Hezbollah leader, Sheikh Hassan Nasrallah, who said in a televised speech: "If you bomb our capital Beirut, we will bomb... Tel Aviv."

Security sources in Israel told a BBC correspondent that "if Tel Aviv was hit by Hezbollah rockets, Israel would target infrastructure in Lebanon".

In his speech Sheikh Nasrallah also said that Hezbollah would end its rocket attacks if Israel stopped attacking what he called civilian areas in Lebanon.

Israeli ambassador to the United Nations Dan Gillerman said that suggestion was "a sign of weakness" and that Hezbollah might be "looking for a way out".

Although UN delegates remained optimistic of agreement on a ceasefire resolution soon, there remained differences on the wording.

"We're certainly getting close [to a resolution] within days," said US Secretary of State Condoleezza Rice.

French Foreign Minister Philippe Douste-Blazy said he believed a durable ceasefire would be in place soon.

Landmines

Lebanese Prime Minister Fouad Siniora on Thursday called for a lasting solution to the conflict.

Speaking on the BBC's Newsnight programme, he said Israel had to withdraw from the disputed border territory known as the Shebaa Farms, which the UN says is part of Syria.

Mr Siniora said he wanted international leaders to pressure Israel to return detainees, provide maps of landmines and withdraw from "occupied territory".

Then, he said, "we will arrange that they will get back the abducted soldiers" and ensure that "there won't be any weapons in Lebanon other than those of the Lebanese authorities".

In other developments:

• The UN's refugee agency (UNHCR) warned that fuel shortages were increasingly hampering humanitarian relief operations in Lebanon
• Venezuelan President Hugo Chavez recalled his ambassador from Israel, calling the attacks on Lebanon "genocide"
• King Abdullah of Jordan publicly criticised the US and Israel over the fighting in Lebanon

Prime Minister Ehud Olmert has said there will be no ceasefire until an international force is deployed in southern Lebanon.

A second UN resolution would probably be needed to authorise the international peacekeeping force.

Since such a force could take weeks or months to arrive, a smaller force of French soldiers may be sent in first, BBC security correspondent Frank Gardner notes.

BBC