BEIRUT, Lebanon — Israel's pounding of Hezbollah positions across Lebanon expanded today with missiles targeting bridges in the Christian heartland north of Beirut for the first time, an attack that further isolates Lebanon from the outside world.

Five civilians were killed and 19 wounded in the airstrikes north of the capital, Lebanese security officials said. A Lebanese soldier and four civilians were killed in air raids near Beirut's airport and southern suburbs, security officials and witnesses said.

The destruction of four bridges on the main north-south coastal highway linking Beirut to Syria further sealed Lebanon from outside links, as the Israeli naval blockade and earlier strikes against roadways have largely closed off other access points.

Fierce fighting continued along the border, and Hezbollah said in a statement broadcast by the group's Al-Manar TV station that guerrillas had killed six Israeli soldiers near the villages of Aita al-Shaab and Markaba.

Arab media reported Hezbollah had hit an Israeli tank. The Israeli army was not immediately available to comment on the claims.

The clashes came a day after a massive barrage of guerrilla rockets pounded northern Israel, killing eight people, and an offer by Hezbollah's leader to stop the attacks if Israel ends its airstrikes. Two more rockets hit northern Israel early today, causing little damage.

Israel's United Nations ambassador, Dan Gillerman, said that Sheik Hassan Nasrallah's offer of a truce was "a sign of weakness ... and he may be looking for a way out."

Gillerman warned against Hezbollah threats to launch rockets on Israel's commercial center of Tel Aviv. "We are ready for it, and I am sure that he (Nasrallah), as well as his sponsors, realize the consequences of doing something as unimaginable and crazy as that," the Israeli ambassador told CNN early today.

The Israeli military said the targets of the latest attacks in the southern Beirut suburb of Dahieh were Hezbollah facilities and a Hamas office. Beirut media said Israel launched 24 bombing runs in an hour.

South Beirut has been attacked repeatedly by Israeli warplanes since fighting began July 12. It is predominantly a Shiite Muslim sector largely controlled by Hezbollah guerrillas, and Israel has not struck Beirut proper since the start of the war.

However, the strikes early Friday hit the affluent Christian locality of Jounieh, north of the capital, for the first time. The bombing against the picturesque coastal resort marked a sharp expansion of Israel's attack on Lebanon, which now threatens Christian areas where Hezbollah has no support and no presence.

In the hills of southern Lebanon, Israeli artillery intensified bombing overnight, sometimes sending as many as 15 shells per minute against suspected Hezbollah strongholds.