Both Obama and United Nations officials also called on Israel to open Gaza border crossings.

"As part of a lasting ceasefire, Gaza's border crossings should be open to allow the flow of aid and commerce," Obama said, during his first visit to the State Department as president.

UN humanitarian chief John Holmes said the borders must be opened to allow reconstruction of the enclave.

"You have to have cement and construction materials and pipes and spare parts," he said at a UN-run school hit by an Israeli missile in the northern Gaza town of Beit Lahiya.

Since Israel began its 22-day offensive on December 27, the army said it had allowed 2,284 truckloads of humanitarian supplies into Gaza where the 1.5 million population relies on the border crossings for virtually everything.

Obama said his administration would "actively and aggressively seek a lasting peace between Israel and the Palestinians, as well as Israel and its Arab neighbors."

The President confirmed George Mitchell, a veteran diplomat renowned for negotiating the 1998 Good Friday agreement that helped bring peace to Northern Ireland, as his Middle East envoy.

He said he would be sending the former senator "to the region as soon as possible to help the parties ensure that the ceasefire that has been achieved is made durable and sustainable."

In a call to Palestinian president Mahmud Abbas, new US Secretary of State Hillary Clinton also vowed to work for a "durable and just peace as quickly as possible," Abbas spokesman Nabil Abu Rudeina told AFP.

Israel pounded the Gaza Strip for 22 days to reduce the threat from the Islamist group Hamas, before ceasefires on both sides came into effect this week.

But the Jewish state warned it would attack the territory again if Hamas uses smuggling tunnels under the Egyptian border to rearm.

"Things must be clear - Israel reserves the right to react militarily against the tunnels once and for all," Foreign Minister Tzipi Livni said.

Her ministry said Livni told Clinton in a phone conversation that peace talks with the Palestinians should resume as soon as possible.

Livni stressed the necessity for a resumption of negotiations with Abbas, omitting Hamas.

A senior aide to Abbas, whose forces were booted out of Gaza by Hamas in May 2007, said that the Islamists would not be allowed to turn Gaza into a separate entity in the wake of the war.

"We will not allow the creation of a separatist entity, no matter what the price," Yasser Abed Rabbo told a press conference. "The plot aiming to separate Gaza from the West Bank will not pass."

Two women, two children and an elderly man were wounded on Thursday by fire from Israeli navy boats patrolling the Mediterranean, medics said. The army said it fired warning shots at a fishing boat.

Four Palestinians were injured when two tunnels on the Gaza-Egypt border collapsed, an Egyptian security official said on Thursday.

On Thursday morning a tunnel caved in, injuring Palestinian Sharif al-Shaer, in his 20s, who was hospitalised with broken bones and respiratory problems, he said.

Earlier the security official said another tunnel had collapsed on Wednesday and that three Palestinians were hospitalised in Egypt for respiratory problems.

During its offensive on Hamas, Israel bombed hundreds of tunnels on the Gaza-Egypt border, destroying 150, according to Defence Minister Ehud Barak.

Israel declared a ceasefire on Sunday after guarantees from Cairo and Washington to secure the enclave's porous border with Egypt.

In a final casualty toll, Gaza medics said the Israeli offensive had killed 1330 people, at least half of them civilians, including 437 children. Another 5450 were wounded, including 1,890 children.

A prominent Al-Qaeda figure, Abu Yahya al-Libi, on Thursday urged Islamist militants to launch attacks in the West, naming the United States and Britain, to avenge Israel's onslaught on Gaza, according to a translation by SITE monitoring group of his video clip posted on the Internet.