The Israeli military says its forces have resumed ground operations in the central and southern Gaza Strip, as a second day of airstrikes killed at least 38 Palestinians, according to local health workers.
The renewed ground operations come a day after in one of the deadliest episodes since the beginning of the war in October 2023, and the first major escalation since a fragile ceasefire began almost two months ago.
The Israeli military said it had "begun targeted ground operations in the central and southern Gaza Strip to expand the security perimeter and create a partial buffer between the north and south".
It said its operations have extended Israel's control over the Netzarim Corridor, which bisects Gaza, and were a "focused" manoeuvre.
Palestinian militant group Hamas said the ground operation and the incursion into the Netzarim Corridor were a "new and dangerous violation" of the two-month-old ceasefire agreement. In a statement, the group reaffirmed its commitment to the deal called on mediators to "assume their responsibilities".
UN says worker killed in Israeli airstrike
It comes as the United Nations said an Israeli airstrike had killed a foreign staffer and wounded five workers at the site of a UN headquarters in central Gaza City. But Israel denied this, saying it had hit a Hamas site, where it had detected preparations for firing into Israeli territory.
Jorge Moreira da Silva, executive director of the UN Office for Project Services, said: "Israel knew that this was a UN premises, that people were living, staying and working there, it is a compound. It is a very well-known place."
UN secretary-general António Guterres called for a full investigation and condemned all attacks on UN personnel. In a statement, he said the strike brought the number of UN colleagues killed in Gaza since 7 October 2023 to at least 280.
In Sofia, the foreign ministry said a Bulgarian working for the UN died on Wednesday in Gaza, citing preliminary information. It was not immediately clear if the Bulgarian was the foreign UN staffer killed in Gaza.

UN secretary-general António Guterres called for a full investigation and condemned all attacks on UN personnel. Source: AAP
In the latest violence, local health workers said an Israeli airstrike killed four people and wounded 10 others in a house in the northern Gaza Strip town of Beit Hanoun, where the army renewed evacuation orders to residents earlier on Wednesday.
In Beit Lahiya, a new Israeli airstrike killed 14 people at a mourning tent, medics said.
Israel and Hamas accuse each other of breaching the truce, which had offered a respite for Gaza's 2.3 million residents after 17 months of war.
Much of the enclave now lies in ruins after Hamas' 7 October 2023 attack, in which more than 1,200 people, including an estimated 30 children, were killed and over 200 hostages taken, according to the Israeli government. More than 49,000 people have been killed in Gaza since October 7, according to the health ministry in Gaza.
in the long-standing conflict between Israel and Hamas.
Israel has accused Hamas of using Palestinian civilians as human shields. Hamas denies this and accuses Israel of indiscriminate bombings.
Prime Minister Benjamin Netanyahu's decision to resume bombardments has triggered protests in Israel as 59 hostages are still held in Gaza, with 24 of them believed to be still alive.
A coalition of hostage families and protesters against Netanyahu's moves against the judiciary and other parts of the security establishment has regrouped and accuses the prime minister of using the war for political ends.
Palestinian medics said Israeli tank shelling on the main north-south Salahuddin Road killed one Palestinian and wounded others.
Hamas spokesperson Abdel-Latif Al-Qanoua told Reuters the closure of the Salahuddin Road was a "total coup" against the three-phase ceasefire agreement and a tightening of the blockade on Gaza.
He said the group would welcome any proposal "as long as it is based on launching negotiation on the second phase and a complete end to the war in Gaza".
Earlier on Wednesday, the Israeli army dropped leaflets in the northern and southern Gaza Strip, once again ordering residents to evacuate their homes. Defence Minister Israel Katz issued a video statement warning Gaza residents that evacuation from combat zones would begin shortly.
He said airstrikes were "only the first step" and if the hostages were not released, "Israel will act with force you have not yet seen".
Western leaders respond
The renewed violence was condemned by Western nations, including France and Germany, as well as Qatar and Egypt, which had been acting as mediators in the ceasefire negotiations.
Israel and Western powers do not want Hamas to play any role in the enclave when the war is over.
Arab nations drew up a plan for peace and reconstruction in Gaza after a proposal from United States President Donald Trump to resettle Palestinians and turn it into a "Riviera" of the Middle East triggered outrage in the region. However, the plan has not gained traction.
European Union foreign policy chief Kaja Kallas said on Wednesday she told Israeli Foreign Minister Gideon Saar that the situation in Gaza was "unacceptable".
Jordan's King Abdullah called for the ceasefire to be restored and for aid flows to resume.
"Israel's resumption of attacks on Gaza is an extremely dangerous step that adds further devastation to an already dire humanitarian situation," he said on a visit to Paris for talks with French President Emmanuel Macron.
However, Dorothy Shea, acting US ambassador to the United Nations, said on Tuesday the blame for the resumption of hostilities "lies solely with Hamas".