But, with exits to Israel and Egypt shut, the retaliatory military operations have effectively turned the narrow 25-mile long Gaza Strip into a kill box. More than 1,500 people have already died in the bombing campaign, a third of them children, and another 6,600 are wounded, according to Gaza’s Health Ministry.

“In the following days, the IDF will continue to operate significantly in Gaza City,” the Israel Defense Forces said, adding that Hamas militants were hiding in tunnels beneath civilian homes and in heavily populated areas. “Civilians of Gaza City, evacuate south for your own safety and the safety of your families and distance yourself from Hamas terrorists who are using you as human shields.”

Hamas dismissed the warnings and told citizens to stay. “Our Palestinian people reject the threat made by the leaders of the occupation and its call for Gazans to leave their houses and leave to the south or to Egypt,” the group said, describing the evacuation order as “psychological war.”

In a briefing, IDF spokesman Rear Adm. Daniel Hagari retorted that whatever now happened to Gaza residents was the responsibility of Hamas for telling them not to leave.

Hamas has also continued to fire rockets at Israel throughout the crisis; most appear to have been intercepted by the Iron Dome defense system, though dozens have needed medical treatment.

The United Nations said that the evacuation that Israel was urging was not only unfeasible, but risked worsening an already dire situation. “The United Nations strongly appeals for any such order, if confirmed, to be rescinded avoiding what could transform what is already a tragedy into a calamitous situation,” it said in a statement.

It was unclear Friday how many civilians had heeded the call to leave. The Palestinian Red Crescent Society, whose ambulances have repeatedly been targeted by Israeli strikes, said the Ministry of Health had decided not to evacuate the area’s hospitals.

“No one will be able to evacuate the patients and injuries who are in the ER room connected to medical devices, it’s an impossible mission,” said Nebal Farsakh, a spokeswoman for the Red Crescent.

The Norwegian Refugee Council, an international aid agency operating in the territory, said the evacuation order, which came without clear guarantees of safety and return, “would amount to the war crime of forcible transfer.”

Nancy Okail, president of the Washington-based Center for International Policy, described the evacuation order as not only impossible, but “a license to kill. Because those who remain behind, it would be sort of a warranty to kill those who stay.”

Tensions are also high in the occupied West Bank, where Hamas has called for a “Day of Rage” on Friday in support of Gaza, and demonstrations are expected across the territory, especially as the civilian casualties mount. Since Saturday, 35 Palestinians have been killed there by Israeli soldiers and settlers, adding to the more than 200 killed this year in the West Bank, the highest annual toll in two decades.

In the midst of the crisis, U.S. Secretary of State Antony Blinken flew from Israel to meet King Abdullah II of Jordan in Amman on Friday and discuss the growing crisis, including “efforts to secure the release of all hostages and prevent the conflict from widening,” said State Department spokesman Matt Miller.

Blinken “underscored that Hamas does not stand for the Palestinian people’s right to dignity and self-determination and discussed ways to address the humanitarian needs of civilians in Gaza while Israel conducts legitimate security operations to defend itself from terrorism,” Miller said.

The spokesman did not address the evacuation order directly. Officials familiar with the situation said that Israel had informed the United States on Thursday that it wanted to get as many civilians as possible out of Gaza City before launching a ground operation, but did not warn Blinken of the specific plan to call for the evacuation of 1.1 million people.

But in a separate statement, Jordan’s king warned Israel against “any attempt to forcibly displace the Palestinians from all the Palestinian Territories or to cause their internal displacement, calling for preventing a spillover of the crisis into neighbouring countries and the exacerbation of the refugee issue.”

He also stressed the need to open humanitarian corridors to allow for the provision of food and medicine.

Blinken will go on to meetings in Qatar, Bahrain, Saudi Arabia, the United Arab Emirates and Egypt. U.S. officials are hoping to convince allies who have sway with Iran and Hezbollah to refrain from entering the conflict. Officials spoke on the condition of anonymity to discuss a sensitive situation.

The IDF said Friday morning that it struck 750 military targets overnight, including compounds, guard posts and underground tunnels belonging to Hamas, as well as the residences of senior operatives.

Hamas’s military wing said Friday that 13 of its hostages had been killed by airstrikes within the past 24 hours. “Six of them were killed in separate locations in the northern governorates, and seven were killed in three different locations in the Gaza governorate,” the al-Qassam Brigades said in a statement, which was not possible to independently verify. The whereabouts of the hostages, some of them toddlers, are not publicly known.

Loveluck reported from London. Claire Parker in Cairo and Sarah Dadouch in Beirut contributed to this report.