Updated

The U.N. chief on Friday urged Hamas to end its rocket attacks on Israel and told Israeli leaders to exercise maximum restraint.

Ban Ki-moon has been calling international and Middle East leaders in a bid to de-escalate the crisis that erupted this week and intends to visit the region shortly, his spokesman said. Martin Nesirky said the secretary-general "is extremely concerned about the continued violence in Gaza and Israel, and deeply worried by the rising cost in terms of civilian lives."

"He urgently appeals to all concerned to do everything under their command to stop this dangerous escalation and restore calm. Rocket attacks are unacceptable and must stop at once. Israel must exercise maximum restraint," Nesirky told reporters.

Ban's "paramount concern is for the safety and well-being of all civilians. All sides must respect their obligations under international humanitarian law in this regard," his spokesman said.

"A new cycle of bloodshed will make neither Israelis nor Palestinians more secure. Nor will bloodshed open the door to negotiations that could achieve the two-state solution necessary to end such violence permanently," Ban said through his spokesman.

Nesirky would not comment on questions about where Ban would travel in the region, and whether he would visit Gaza or Israel.

On Wednesday, the Security Council held a closed-door emergency meeting on Gaza, but did not issue any formal statement or take any action. The council did not have any further meeting on Gaza scheduled as of Friday afternoon.

At least 23 Palestinians, including 12 militants and six children, as well as three Israelis have been killed in the fighting.

The dead included a teacher who worked for the U.N. Marwan Abu El Qumsan, who was in his early 50s and taught Arabic at a school run by the U.N. Relief and Works Agency for Palestine Refugees in the Near East in Jabalia, was killed Wednesday. The agency said the violence in Gaza forced it to close its schools temporarily.

The UN Office for the Coordination of Humanitarian Affairs said Thursday that the escalating violence has triggered widespread fear on both sides of the border, and the humanitarian situation in Gaza "remains precarious."