UN Secretary-General Ban Ki-moon has condemned the killing of dozens of Palestinians in the Gaza Strip by Israeli shelling as an "atrocious action" and called for an immediate end to almost two weeks of fighting.

Ban's comments on Sunday came before a UN Security Council emergency meeting on Gaza early on Monday that was convened on the request of Jordan.

It also comes as US Secretary of State John Kerry is heading back to the Middle East as the Obama administration attempts to bolster regional efforts to reach a ceasefire.

The State Department said Kerry would leave on Monday for Egypt where he will join diplomatic efforts to resume a truce that had been agreed to in November 2012.

Ban, in Doha on the first leg of a Middle East tour to try to end the bloodshed that has cost more than 400 lives, met Qatar's Emir Sheikh Tamim bin Hamad al-Thani, Palestinian President Mahmoud Abbas and Qatari Foreign Minister Khaled al-Attiyah before heading for Egypt.

"While I was on route to Doha, dozens more civilians have been killed in the Israeli military strikes ... in Gaza ... I condemn the atrocious action," he said in a statement after talks with Attiyah.

"Israel must exercise maximum restraint. I repeat my demands to all sides that they must respect international humanitarian law. The violence must stop now," he added.

More than 60 Palestinians and 13 Israeli soldiers were killed as Israel shelled Gaza's Shujayea neighbourhood and battled Hamas fighters in the bloodiest fighting in the 13-day offensive.

The US Department of State said that two of the Israeli soldiers were US citizens. It was not immediately clear whether they also held Israeli citizenship.

Attiyah called the killings a massacre and said Israel must not be allowed to choose when to wage a war and when to stop.

"We condemn all the atrocities perpetrated by Israel against the Palestinian people, the last of which was al-Shujayea massacre today," Attiyah said. "The majority of the victims were women and children."

Israeli soldier 'captured'

Hamas' armed wing al-Qassam brigades said they had taken an Israeli soldier, named Shaul Aron, captive late on Sunday, a claim Israel has denied.

"When they decided on this operation they have to expect that their soldiers may be killed, captured, or injured," senior Hamas official and spokesman Osama Hamdan told Al Jazeera.

In an appeal filmed in Doha, Palestinian President Abbas called on the international community to protect Palestinians against what he called the current "unbearable" situation.

"The UN security council has failed to protect Palestinians and I call on the council to hold an emergency meeting today to protect Palestinians ... what Israel did today is a crime against humanity," he said in the recording shown to reporters.

He further called for an immediate ceasefire and stressed unity among all factions in the Palestinian territories.

Hamas says any accord must include lifting a blockade imposed by Israel and Egypt on the Gaza Strip and a return to an understanding that ended a previous round of fighting in 2012.

"There was an Egyptian proposal, which was not accepted by the Palestinians because there were no guarantees for a ceasefire, there were no guarantees for lifting the siege on Gaza and stopping the violations in the West Bank," Hamdan told Al Jazeera.

"I am looking forward to a model better than 2012. The events now are worse, the attack is worse - Israel has violated the 2012 ceasefire, so we need more guarantees from the Israeli side and the international community," Hamdan said.