Israeli tanks and warplanes continued the offensive in Gaza Thursday, hitting the Jabaliya refugee camp where police said an infant boy was among the dead.

Most of the casualties were reported in the southeast Gaza town of Khan Younis. Ambulances struggled to enter the area amid intense fighting between Israeli troops and Hama fighters, according to Al Jazeera’s correspondent.

The new toll came after the U.S.’s Federal Aviation Administration lifted its flight ban on American airlines for Israel’s main airport late Wednesday and the U.N.’s top human rights official warned that the killing of Gazan civilians and children in Israeli airstrikes may amount to war crimes.

Navi Pillay, the international body’s high commissioner for human rights, on Wednesdsay told an emergency debate on the crisis that there was “a strong possibility that international law had been violated” during the weeks-long conflict, citing the shelling of homes and hospitals in the coastal enclave. She also condemned the indiscriminate firing of rockets and mortars into Israel by Palestinian fighters. The U.N. Human Rights Council (UNHRC) later agreed to launch an independent inquiry into allegations that international law had been violated in the course of the Gaza airstrikes.

Israel blasted the UNHRC's call, saying it's decision was a "travesty and should be rejected by decent people everywhere."

“Rather than investigate Hamas, which is committing a double war crime by firing rockets at Israeli civilians while hiding behind Palestinian civilians, the UNHRC calls for an investigation of Israel, which has gone to unprecedented lengths to keep Palestinian civilians out of harm's way," a statement from the Israeli Prime Minister’s office read.

The remarks come a day after Israel received a psychological blow in its ongoing military operation in the shape of a decision by the U.S.’s Federal Aviation Administration (FAA) to ban all American airlines from flying in and out of Israel’s main airport for 24 hours. The move, extended on Wednesday for an additional 24 hours, was prompted by security fears following a Hamas rocket attack near Ben Gurion International Airport on Tuesday. The flight ban has been echoed in Europe, where airlines likewise grounded planes headed to the country.

Mindful of the potential economic impact of the move, Israeli Prime Minister Benjamin Netanyahu reportedly appealed to the United States to rethink the cancellation of flights.

The FAA lifted the ban late Wednesday night. "Before making this decision, the FAA worked with its U.S. 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.

Air France said it was suspending its flights "until further notice" and Germany's two largest airlines — Lufthansa and Air Berlin —on Wednesday cancelled more flights to Tel Aviv.

Meanwhile, U.S. Secretary of State John Kerry flew to Israel on Wednesday in the latest push to broker a cease-fire between Israel and Hamas.

America’s top diplomat indicated that the negotiations were making some progress despite the ongoing violence on the ground, offering a glimmer of hope that more than two weeks of bloodshed could be ended.

"We have certainly made some steps forward," Kerry said in Jerusalem, where he was meeting for the second time this week with U.N. chief Ban Ki-moon. "There's still work to be done."

Ban said he and Kerry were jointly lobbying officials in the region to push Hamas and Israel to a cease-fire as soon as possible. "We do not have much time to wait and lose," Ban told reporters before the meeting with Kerry.

Kerry then headed to Ramallah in the West Bank, where he retierated his call for a cease-fire.

Speaking alongside Palestinian President Mahmoud Abbas after their meeting, Kerry said, “I can tell you that we have, in the last 24 hours, made some progress in moving towards that goal."

Kerry also met with Netanyahu on Wednesday, and will return to Cairo before the day's end.

U.S. officials have downplayed expectations for an immediate, lasting truce between Israel and Hamas, which controls Gaza. Instead, Kerry's mission seems more focused on defining the limits of what each side would accept in a potential cease-fire.

Israel and the U.S. back an unconditional cease-fire proposal that has been offered by Egypt, which would be followed by talks on a possible new border arrangement for Gaza.

But Hamas has said it was not consulted over Egypt’s truce plan, first launched last week, and indicated that certain conditions would have to be met as part of any cease-fire. Specifically, the group has demanded a lifting of a crippling blockade on the enclave before halting fire.

Hamas political leader Khaled Meshaal reiterated that call on Wednesday, saying the group was prepared to accept a humanitarian truce in Gaza but not until Israel lifted its blockade.

"Everyone wanted us to accept a ceasefire and then negotiate for our rights, we reject this and we reject it again today," he said at a news conference in Qatar.

The blockade has seen Israel and Egypt severely restrict movement in and out of Gaza since 2007.

In addition to discussions with Egyptian officials, including President Abdel Fattah El Sisi, Kerry spoke several times Tuesday from Cairo with Turkish Foreign Minister Ahmet Davutoglu and Qatari Foreign Minister Khalid al-Attiya. Both Turkey and Qatar have better relations with Hamas, and either could serve as a mediator in any negotiations.

Egypt has also been negotiating with some Hamas officials, but relations between the two sides have been strained since Egypt outlawed the Muslim Brotherhood, which has ties to Hamas, after last year's overthrow of President Mohamed Morsi.

The diplomatic efforts for a breakthrough take place amid a backdrop of continued violence and rising civilian deaths.

Wednesday’s deaths bring the number of Palestinians killed during the 16-day Israeli assault on Gaza to 718, including scores of children. More than 4,563 people have been injured.

The number of Israelis who have died has climbed to 35 — three civilians and 32 soldiers. One other soldier remains missing but is presumed dead, according to the Israeli army.

Al Jazeera and wire services