Israel has carried out air strikes and small-scale incursions into Lebanon, as troops and tanks gather on the border.
Air strikes on TV masts disrupted broadcasts
Israeli jets knocked out TV and phone masts in the east and north of Lebanon, while ground troops carried out operations in two southern villages.
Israel has warned residents in 10 southern villages to leave by 1800 local time (1500 GMT), and thousands of civilians have been fleeing north.
However, Israel has insisted it has no plans for a large-scale invasion.
UN humanitarian chief Jan Egeland is due to arrive in Beirut to assess the crisis on the ground.
Mr Egeland said half a million people needed assistance - and the number was likely to grow.
He is expected to call on Israel to guarantee safe passage by land, sea and air for humanitarian supplies.
On the 11th day of the air campaign against Lebanon, Israel continued its assault, saying it was targeting Hezbollah rocket launchers and command posts, along with roads linking Lebanon to Syria.
The militant group continued to fire dozens of rockets into Israel, with an estimated 25 missiles landing in and around Israel's northern town of Kiryat Shmona, injuring six people.
Hezbollah has continued to fire rockets into Israel
Israeli planes hit at least two communications and TV transmission towers - one in the Kesrwan mountains, east of Beirut, and in Terbol in northern Lebanon.
The strike disrupted broadcasts for Hezbollah's Al-Manar television and the Lebanese Broadcasting Corporation.
An Israeli military spokesman said the television and mobile phone networks were being used to spread the militant group's propaganda.
Israeli soldiers are continuing some ground incursions into Lebanon, and briefly occupied two southern villages, Maroun al-Ras and Marwahin.
Six Israeli soldiers were killed in three days of fighting in Maroun al-Ras.
Despite the troop build-up on the border, Israel's army chief of staff has said any fresh incursions would be limited in scope.
The army said raids across the border would continue, targeting Hezbollah bunkers and tunnels that could not be destroyed from the air.
Correspondents say Israeli troops are likely to push deeper and more frequently into Lebanon over the coming days.
US Secretary of State Condoleezza Rice is travelling to the Middle East on Sunday, as is German Foreign Minister Frank Walter Steinmeier, who helped broker a prisoner exchange between Israel and Hezbollah in 2004.
Lebanese civilians have been trying to escape the Israeli strikes
The crisis was triggered by the capture of two Israeli soldiers by Hezbollah militants on 12 July.
The Israeli air force says it has hit 70 targets in Lebanon since Friday night, and 1,800 targets over the course of the campaign.
The BBC's Martin Asser travelled south on the main road between Beirut and Tyre, close to the Israeli border. He passed hundreds of cars heading north, packed with families fleeing the area.
Many cars were flying white flags to show they were civilians.
Israeli government spokesman Avi Pazner told the BBC Israel was not interested in invading, conquering or occupying Lebanon, from where it withdraw troops in 2000.
"We only want to get rid of Hezbollah," he said.
It is thought Israel wants to set up a deep buffer zone in southern Lebanon to try to stop Hezbollah from using the area to launch rocket attacks.
But senior Lebanese officials have warned the country's army will go into battle if Israel invades.
At least 349 Lebanese have been killed in the 11 days of violence, many of them civilians.
Thirty-four Israelis have been killed, including 15 civilians killed by rockets fired by Hezbollah into Israel.