"There is no need for a 72-hour temporary ceasefire because Israel has opened a humanitarian corridor to and from Lebanon," said Israeli government spokesman Avi Pazner.
UN emergency relief co-ordinator Jan Egeland had asked for the pause in fighting so relief workers could move elderly, young and wounded people out of the area near the border.
Pazner said Israel was not stopping aid from reaching south Lebanon.
"The problem is completely different," he said. "It is Hezbollah, which is deliberately preventing the transfer of medical aid and food to the population of southern Lebanon in order to create a humanitarian crisis, which they want to blame Israel for."
But on Friday, the international medical charity Medecins Sans Frontieres said "in effect there is no real humanitarian access in the south".
Washington has pledged $30 million to help Lebanon but has refused to back an immediate ceasefire between the two sides.
"They send the Israelis smart bombs and they send us blankets. If it was up to me, I wouldn't let this ship dock here. I would dump this stuff in the sea," said a Lebanese soldier watching US aid being unloaded in Beirut.
A US military catamaran had brought blankets, tarpaulins and medical kits for some of the 800,000 people displaced by the war.
Condoleezza Rice, the US secretary of state, has welcomed as a "positive step" the agreement by Hezbollah cabinet members to seek an immediate ceasefire that would include the disarming of militias.
Speaking to reporters in Doha on her way to Jerusalem, Rice praised Fouad Siniora, the Lebanese prime minister, for hammering out the deal.
On Thursday, the Lebanese cabinet, which includes two ministers from Hezbollah, unanimously approved seven points that Siniora had made to the international conference in Rome on Wednesday.
The points included extending the authority of the state across the whole country and boosting international forces in the south to help the Lebanese army take control of the area.
Rice said she was ready for "fairly intense" talks on the conflict but refused to set a deadline for a resolution.
"As we want an early end to the violence it is important that we get agreement on the elements," she said.
At least 462 people have been killed in Lebanon since the conflict began on July 12.
Hezbollah, which wants to swap the soldiers for Lebanese and Palestinian prisoners held by Israel, has killed 51 Israelis, 18 of them civilians hit by rockets fired into the Jewish state.