Less than three weeks ago, Israeli Prime Minister Benjamin Netanyahu sat beside President Joe Biden and marveled that a "historic peace between Israel and Saudi Arabia" seemed within reach — a diplomatic advance that he predicted could lead to lasting peace between the Israelis and Palestinians.

Biden was equally optimistic, telling Netanyahu during their meeting in New York, "If you and I — 10 years ago — were talking about normalization with Saudi Arabia, I think we'd look at each other like, 'Who's been drinking what?'"

Israeli warplanes pounded downtown Gaza City, home to Hamas' centers of government, with relentless bombardments into early Tuesday, after Israel's prime minister vowed retaliation against the Islamic militant group that would "reverberate for generations."

The 4-day-old war has already claimed at least 1,600 lives, as Israel saw gun battles in the streets of its own towns for the first time in decades and neighborhoods in Gaza were reduced to rubble. Hamas also escalated the conflict, pledging to kill captured Israelis if strikes targeted civilians without warning.

A senior Hamas official has said only a small number of top commanders inside Gaza knew about the wide-ranging incursion launched into Israel, but that allies like Iran and Hezbollah "will join the battle if Gaza is subjected to a war of annihilation."

Ali Barakeh, a member of Hamas' exiled leadership, spoke to The Associated Press in his Beirut office as Israel bombarded Gaza and vowed a total blockade of the Hamas-ruled territory.

Egypt intensified its push Monday for diplomatic efforts to de-escalate spiralling violence in Gaza and Israel, his office said, after three days of fighting killed more than 1,200 people.

President Abdel Fattah al-Sisi, whose country has historically been a key mediator between Israel and the Palestinians, spoke with UAE Mohamed bin Zayed Al Nahyan, agreeing to "intensify discussions and diplomatic efforts to stop military escalation", Sisi's spokesman said.

Israeli air strikes on Gaza have killed four "prisoners" held by Hamas, said Monday the Palestinian militant group whose fighters carried out a surprise attack on Israel over the weekend.

"The occupation's bombing last night and today on the Gaza Strip led to the killing of four of the enemy's prisoners," the Ezzedine al-Qassam Brigades, the armed wing of Hamas, said on its website.

For Palestinians in Gaza, Israel's eyes are never very far away. Surveillance drones buzz constantly from the skies. The highly-secured border is awash with security cameras and soldiers on guard. Intelligence agencies work sources and cyber capabilities to draw out a bevy of information.

But Israel's eyes appeared to have been closed in the lead-up to an unprecedented onslaught by the militant Hamas group, which broke down Israeli border barriers and sent hundreds of militants into Israel to carry out a brazen attack that has killed hundreds and pushed the region toward conflict.

Qatar is mediating an urgent prisoner swap between Hamas and Israel, a Hamas source said.

"With U.S. support, Qatar is seeking to accomplish an urgent agreement that would lead to the release of Israeli women captured by Hamas (during Operation Al-Aqsa Flood) in exchange for Palestinian female prisoners in Israeli prisons," the source, who wished to remain anonymous, told Chinese news agency Xinhua.

The evacuation warning came shortly after dark. The Israeli military fired the shot just a short distance from Nasser Abu Quta's home in the southern Gaza Strip, a precautionary measure meant to allow people to evacuate before airstrikes.

Abu Quta, 57, thought he and his extended family would be safe some hundred meters (yards) away from the house that was alerted to the pending strike. He huddled with his relatives on the ground floor of his four-story building, bracing for an impact in the area.

Moscow and the Arab League will work to "stop the bloodshed" in Israel and Gaza, Russian foreign minister Sergei Lavrov said Monday as he met the group's chief Ahmed Aboul Gheit in Russia.

"I am sure that Russia and the Arab League (will cooperate) above all else to stop the bloodshed," Lavrov said. Aboul Gheit said the Arab League "condemns violence, but from all sides."

Israeli Defense Minister Yoav Gallant Monday ordered a "complete siege" on the Gaza Strip as the military pounded the Palestinian enclave with air strikes.

"We are putting a complete siege on Gaza... No electricity, no food, no water, no gas -- it's all closed," Gallant said in a video statement, referring to the crowded enclave home to 2.3 people.