The US state department has dismissed as "outrageous" a suggestion by Israel that it has been authorised by the world to continue bombing Lebanon.
Israel's forceful campaign has caused fury in some countries
"The US is sparing no efforts to bring a durable and lasting end to this conflict," said spokesman Adam Ereli.
Israeli Justice Minister Haim Ramon made the suggestion after powers meeting in Rome refrained from demanding an immediate ceasefire.
UK PM Tony Blair has arrived in Washington for talks on the crisis.
His meeting with US President George W Bush comes amid growing pressure for the UK and US to join calls for an immediate ceasefire between Israel and Hezbollah.
Israel has carried out dozens of fresh strikes on Lebanon. Lebanese officials said at least 12 people had been killed.
Meanwhile at least 50 Hezbollah rockets have landed on northern Israel, hitting towns including Nazareth, Kiryat Shemona and Safed. Seven people have been injured.
Hezbollah said it had fired a new long-range rocket, called the Khaibar-1, into northern Israel.
The militant group said the rocket landed south of the city of Haifa, the deepest strike inside Israel so far.
Israeli police have confirmed that a previously unknown rocket carrying up to 100kg of explosives had struck an area near the town of Afula.
Elsewhere, two mortar rounds hit a convoy of vehicles carrying civilians escaping the violence in southern Lebanon.
The BBC's Jim Muir, who was with the convoy, said two people in a German TV vehicle were wounded when the rounds exploded next to their car.
The convoy, organised by the Australian embassy, was returning to the port city of Tyre from the border village of Rmeish, where hundreds of people have been trapped by the Israeli offensive.
Our correspondent says the cars were clearly marked as a press and civilian convoy, and that individual journalists had been in contact with the Israelis who knew about the journey.
A BBC security adviser travelling in a car behind the German car said he believed the mortar rounds had been fired from the Israeli side.
The Israeli Defence Forces say they do not believe it was one of their mortars but say they are still checking.
At talks in Rome on Wednesday, the US, UK and regional powers urged peace be sought with the "utmost urgency", but stopped short of calling for an immediate truce. That prompted Mr Ramon to declare Israel had received "permission from the world... to continue the operation".
But questioned by reporters on the sidelines of a summit in Kuala Lumpur, Mr Ereli said: "Any such statement is outrageous."
The US has said a ceasefire is only worth it if it can be made to last. Mr Bush reiterated the US's rejection of a "false peace" on Thursday evening.
The BBC's world affairs correspondent, Nick Childs, points out that Mr Bush also emphasised how troubled he was by the mounting casualties, a suggestion - perhaps - that he is increasingly conscious of the price Washington is paying for its closeness to Israel.
According to Mr Blair's official spokesman, the UK leader wants to step up a gear in securing a UN agreement for an international stabilisation force in southern Lebanon.
But the BBC's James Coomersamy in Washington says that for the moment, there has been no sign that either leader is wavering in his much-criticised opposition to the idea of an immediate ceasefire.
Some 425 Lebanese, the vast majority civilians, are confirmed killed in the 17 days of the conflict - but a Lebanese minister has suggested scores more bodies lie under the rubble.
Fifty-one Israelis, including at least 18 civilians, have been killed, mostly by Hezbollah rockets.
The Israeli assault began after Hezbollah captured two Israeli soldiers and killed eight in a cross-border raid on 12 July.
In the latest developments:
- A Jordanian man was killed and at least three other people wounded in one of several strikes in Kfar Joz, close to the southern Lebanese market town of Natabiyeh
- There were multiple strikes on the Bekaa Valley to the east, on villages around Tyre, and roads in the south-east
- Sporadic clashes were reported in Bint Jbeil, where Israel suffered its worst single losses on Wednesday
- Unarmed UN observers have been temporarily relocated from border positions in southern Lebanon after the deaths of four UN observers in an Israeli strike on Tuesday
In Israel, few people still speak of being able to neutralise Hezbollah, our correspondent in Jerusalem Katya Adler says.
Instead Israel speaks of trying to establish a "secure zone" empty of Hezbollah fighters north of the border with Israel.
The Israeli government's announcement that it is calling up three divisions of reservists - said to number between 15,000 to 40,000 - suggests it is preparing for the possibility of a protracted war, our correspondent says.