Gaza fighting raged, displacing thousands more Palestinians in the battered territory as US Secretary of State John Kerry said efforts to secure a truce between Israel and Hamas had made some progress.

US aviation authorities lifted a ban on flights to Tel Aviv which had been in force for two days, prompted by rocket salvoes out of the Gaza Strip, but many other global airlines were avoiding the Jewish state.

Hamas leader Khaled Meshaal, speaking in Qatar, praised the group's fighters, whom he said had made gains against Israel and said he supported a humanitarian truce but a ceasefire would only be acceptable in exchange for easing Gazans' plight.

"Let's agree first on the demands and on implementing them and then we can agree on the zero hour for a ceasefire... We will not accept any proposal that does not lift the blockade... We do not desire war and we do not want it to continue but we will not be broken by it," he said.

Adding to the pressure on Israel, UN High Commissioner for Human Rights Navi Pillay said there was "a strong possibility" that it was committing war crimes in Gaza, where 703 Palestinians, mostly civilians, have died in the fighting, according to Palestinian health officials.

Pillay also condemned indiscriminate Islamist rocket fire out of Gaza and the United Nations Human Rights Council said it would launch an international inquiry into alleged violations.

Israel denied any wrongdoing. "Get lost," Justice Minister Tzipi Livni said on her Facebook page in response to the investigation.

Kerry met Palestinian President Mahmoud Abbas, UN Secretary-General Ban Ki-moon and a grim-faced Israeli Prime Minister Benjamin Netanyahu on Wednesday. He later returned to Egypt, which shares a border with Gaza and has mediated with Islamist Hamas.

"We have certainly made some steps forward. There is still work to be done," said Kerry, on one of his most intensive regional visits since the peace negotiations he had brokered between Netanyahu and Abbas broke down in April.

An Egyptian official said he expected a humanitarian truce to go into effect by the weekend, in time for the Eid Al-Fitr festival, Islam's biggest annual celebration that follows the fasting month of Ramadan.

However, a senior US official played down the Egyptian official's confidence that there would be a truce during Eid, saying this was a US hope but it was by no means locked in.

"It would not be accurate to say that we expect a ceasefire by the weekend," said the US official, who spoke on condition of anonymity. "We are continuing to work on it, but it is not set at this point."

Kerry, who plans to stay in Cairo until Friday, has been working through Abbas, Egypt and other regional proxies because the United States, like Israel, shuns Hamas as a terrorist group. Hamas brushed off the US diplomat's appeal, saying it would not hold fire without making gains.

"Our interest and that of our people is that no agreement should be made before the conditions of factions of resistance are met," Hamas spokesman Sami Abu Zuhri said.

Israel launched its offensive on July 8 to halt rocket salvoes by Hamas and its allies, which have struggled under an Israeli-Egyptian economic blockade on Gaza and been angered by a crackdown on their supporters in the nearby occupied West Bank.

After an aerial and naval bombardment failed to quell the outgunned guerrillas, Israel poured ground forces into the Gaza Strip last Thursday, looking to knock out Hamas's rocket stores and destroy a vast, underground network of tunnels.

"We are meeting resistance around the tunnels ... they are constantly trying to attack us around and in the tunnels. That is the trend," Israeli military spokesman Lieutenant-Colonel Peter Lerner said on Wednesday.

MILITARY LOSSES RISE

Israel announced that three of its soldiers were killed by explosive devices on Wednesday, lifting the army death toll to 32. Three civilians have also been killed in rocket attacks out of Gaza, including a Thai labourer hit on Wednesday.

The military says one of its soldiers is also missing and believes he might be dead. Hamas says it has captured him, but has not released a picture of him in their hands.

Already hurt by mass tourist cancellations, Israel faced increased economic pressure after the US Federal Aviation Administration (FAA) took the rare step on Tuesday of banning flights to Tel Aviv, renewing the order on Wednesday and then cancelling it.

"Before making this decision, the FAA worked with its US government counterparts to assess the security situation in Israel and carefully reviewed both significant new information and measures the Government of Israel is taking to mitigate potential risks to civil aviation," the FAA said in a press release.

US carriers Delta Air Lines, American Airlines Group and United Airlines did not immediately respond to requests for comments outside regular US business hours.

Many other foreign carriers, on heightened alert after a Malaysian airliner was shot down over a combat zone in Ukraine last week, banned flights. Israeli carriers continued to operate.

"Hamas's success in closing the Israeli air space is a great victory for the resistance, a terrible failure for Israel that wrecks the image of Israeli deterrence," said Hamas's Abu Zuhri.

The Tel Aviv stock exchange and shekel currency were flat, with traders showing little concern about the flight stoppages. - Reuters