Israel launched an assault on Gaza's main northern city weeks after pulling back from it, while Washington vowed to take "all necessary action" to defend its troops after they suffered the first deadly strike in the Middle East since the Gaza war began.
A day after three US servicemen on the Syrian-Jordanian border were killed and at least 34 wounded in what Washington called a drone attack by Iran-backed militants, President Joe Biden's administration was under pressure to respond firmly without triggering a wider war.
"The President and I will not tolerate attacks on US forces and we will take all necessary actions to defend the US and our troops," Defense Secretary Lloyd Austin said on Monday at the Pentagon.
Iran denied any role, but the first fatalities in what have been scores of attacks on US forces in the Middle East since the Israel-Hamas war broke out prompted calls from US politicians for a direct response.
Biden has ordered retaliatory attacks on Iranian-backed groups but has so far stopped short of hitting Iran directly.
"Have no doubt - we will hold all those responsible to account at a time and in a manner of our choosing," he said on Sunday.
Inside Gaza, residents said air strikes on neighborhoods across Gaza City killed and wounded many people. While tanks shelled the eastern areas of the city, naval boats fired shells and gun rounds at the beachfront areas in the west, they said.
Israel said late last year that it had largely completed operations in northern Gaza. The push back into Gaza City, where residents reported fierce gun battles near the main Al-Shifa hospital, indicated that the war was not going to plan.
Among those killed were two Palestinian journalists, Essam El-lulu and Hussein Attalah, along with several members of their families, health officials and the journalist union said.
Hamas, for its part, fired its first volley of rockets for weeks into Israeli cities, proving that the militant group running Gaza still had the capability to launch them after nearly four months of war.
The Israeli military said it shot down six of 15 rockets. Hamas said it had fired them to avenge deaths in Gaza. There were no reports of any casualties in Israel, where air raid sirens sounded and explosions of interceptions were heard overhead.
GAZANS SAY ISRAEL IS IGNORING THE WORLD COURT
Gazans said renewed violence in the enclave made a mockery of a ruling last week by the World Court calling on Israel to do more to help civilians. Health officials say 26,637 Palestinians have been killed in the conflict with thousands more bodies likely under the rubble of destroyed buildings.
"The war continues in a dirtier manner," said Gaza City resident Mustafa Ibrahim, a Palestinian human rights activist now displaced with his family in Rafah near the southern border with Egypt, along with more than a million other Gazans.
Israel ordered new evacuations of the most populated areas of Gaza City, but people said communications blackouts meant many would miss them. Israel blames Hamas for the deaths of civilians for operating among them, which the fighters deny.
People in the north have been grinding animal feed to make flour after flour, rice and sugar ran out, part of an aid crisis now exacerbated by a withdrawal of support for the United Nations' aid agency for Palestinian refugees, UNRWA.
The United States and another major donor, Germany, are among countries to have suspended aid to the agency since Friday after Israel said 12 of UNRWA's 13,000 staff in Gaza were involved in the Oct. 7 Hamas attacks on Israel which killed about 1,200 people.
The Israeli report, seen by Reuters, said 190 UNRWA staff were militants, naming 11 of them.
UNRWA, which says more than 150 of its staff have been killed since October and a million Palestinians are sheltering in its buildings, said it would have to end operations within a month if funding was not restored. It said it had promptly fired staff after being alerted to Israel's allegations.
Air strikes also hit the southern city of Khan Younis, main focus of Israel's attack since last week, which has brought fighting deep into territory holding hundreds of thousands of people who had already fled other areas.
Thousands have now been forced to flee again in a desperate exodus. People fled south on foot carrying children and bedding. Suleiman Abusari, a boy in a wheelchair pushed by his father, said his legs were amputated after an Israeli drone hit him.
"My dream was to play football," he said. "They stole my dream."
'NOT OVER THE FINISH LINE'
Biden and other leaders have been pushing for a new temporary ceasefire to allow for the release of hostages held by Hamas and get more aid into Gaza.
Talks on Sunday initiated by Qatar and involving US, Israeli and Egyptian intelligence chiefs were "constructive", Israel said, while adding that "significant gaps" remain.
White House national security spokesman said there was a framework for a hostage deal, but: "We're not over the finish line right yet."
Violence has also engulfed the occupied West Bank, where the Palestinian health ministry said five people were killed by Israeli forces in four incidents in 24 hours. The Israeli military said three were in response to attempted gun, knife or stone-throwing attacks on its soldiers.
Within Israel, the military said an unidentified motorist in Haifa rammed a soldier and then tried to attack him with an axe before being shot.
In neighboring Syria, two people were killed and several wounded in an Israeli attack on the outskirts of the Syrian capital, Iranian and Syrian media said. Iran's ambassador to Damascus denied reports the location was an Iranian military post.
Israel has a longstanding reputation for attacks on Iran-linked targets in Syria. An Israeli military spokesperson declined to comment.
