Top Muslim diplomats have said Israel was "fully responsible" for the "heinous" killing of Hamas political leader Ismail Haniyeh in Iran and warned it could destabilise the region.

The declaration came at the end of an extraordinary meeting of the Saudi-based Organisation of Islamic Cooperation (OIC) called in part by Iran, which has vowed to retaliate for the attack on Haniyeh, setting the Middle East on edge.

Israel and Hamas are still close to a ceasefire deal, the White House insisted, despite growing fears of a regional war following the assassination of a key Hamas leader.

Washington is still engaged in "intense diplomacy" to prevent further escalation after Iran threatened revenge for the killing of Hamas political leader Ismail Haniyeh in Tehran.

Prime Minister Benjamin Netanyahu said Israel was hitting its enemies and "continuing forward to victory" as the country braced for an expected attack by Iran and Hezbollah.

Israel was "determined to defend" itself following threats of retaliation after its killing of a top Hezbollah commander and following the death of Hamas's former chief Ismail Haniyeh.

Yahya Sinwar's appointment as the top leader of Hamas formalizes a role he assumed in the early hours of Oct. 7, when the surprise attack into Israel that he helped mastermind ushered in the bloodiest chapter of the Israeli-Palestinian conflict.

He is seen as a hard-liner with closer ties to Hamas' armed wing than his predecessor, Ismail Haniyeh, who was killed in an explosion in Iran's capital last month that was widely blamed on Israel and could spark an all-out regional war.

By Kristian Coates Ulrichsen, Rice University

When the longtime political chief of Hamas was assassinated in late July 2024, it didn't just leave the entire Middle East on edge. It also created a political headache in Qatar.

As tensions between Israel and Iran escalate, Egypt has issued a safety notice warning all of its carriers to avoid Iranian air space for a three-hour window early Thursday.

A NOTAM, or notice to air missions, that was posted for pilots Wednesday states that all Egyptian carriers should avoid Tehran’s Flight Information Region and that "no flight plan will be accepted overflying such territory" between 1:00 a.m. and 4:00 a.m. GMT Thursday morning.

Ten people including at least four fighters were killed Wednesday when a bomb-laden truck exploded at a checkpoint in Syria's Turkish-controlled northern city of Azaz, a war monitor said.

An AFP correspondent in the area said a booby-trapped truck had detonated at a checkpoint inside the city.

French President Emmanuel Macron has told Israeli Prime Minister Benjamin Netanyahu to "avoid a cycle of reprisals" in the Middle East, his office said, as fears of a regional war soar.

After earlier telling his Iranian counterpart to "avoid a cycle of reprisals that would put the populations and stability of the region at risk", Macron urged Netanyahu in a telephone call on Wednesday to adopt the same reasoning, the French presidency said in a statement.

Fighters backed by Iran and the Syrian government have attacked areas controlled by U.S.-backed fighters in eastern Syria, killing at least two people and wounding others, the main U.S.-backed force in the war-torn country and an opposition war monitor said Wednesday.

The clashes in Syria's eastern province of Deir el-Zour, which borders Iraq, came amid high tension in the region following last week's killings of a top military commander of Lebanon's militant Hezbollah group in Beirut and the leader of the Palestinian Hamas group Ismail Haniyeh in Iran. Israel was blamed for both attacks, and Iran and Hezbollah have vowed to retaliate.

U.S. Ambassador to Japan Rahm Emanuel will skip this year's atomic bombing memorial service in Nagasaki because Israel was not invited, the embassy said Wednesday.

Emanuel will not attend the event on Friday because it was "politicized" by Nagasaki's decision not to invite Israel, the embassy said.