Israeli ground forces are getting closer to “the complete evacuation” of northern Gaza and residents will not be allowed to return home, the Israel Defense Forces (IDF) has said, in what appears to be the first official acknowledgment from Israel it is systematically removing Palestinians from the area.

In a media briefing on Tuesday night, the IDF Brig Gen Itzik Cohen told Israeli reporters that since troops had been forced to enter some areas twice, such as Jabaliya camp, “there is no intention of allowing the residents of the northern Gaza Strip to return to their homes”.

He added that humanitarian aid would be allowed to “regularly” enter the south of the territory but not the north, since there are “no more civilians left”.

International humanitarian law experts have said that such actions would amount to the war crimes of forcible transfer and the use of food as a weapon.

The Israeli army and government have repeatedly denied trying to force the remaining population of northern Gaza to flee to the relative safety of the south during a month-long renewed offensive and tightened siege. Residents still clinging on in the north have said the new operation has created the worst conditions of the war to date. Israel said the push is necessary to combat regrouped Hamas cells.

Rights groups and aid agencies have alleged that despite the denials, Israel appears to be carrying out a version of the so-called “generals’ plan”, which proposes giving civilians a deadline to leave and then treating anyone who remains as a combatant.

It is unclear how many people remain in northern Gaza; last month, the UN estimated there were about 400,000 civilians unable or unwilling to follow Israeli evacuation orders. On Wednesday social media footage showed waves of several dozen displaced people carrying children and rucksacks and walking south through flattened areas of Gaza City.

Many had not eaten in days, Huda Abu Laila told the Associated Press. “We came barefoot. We have no sandals, no clothes, nothing. We have no money. There is no food or drink,” she said.

At least 15 people were killed in an Israeli airstrike on the northern town of Beit Lahiya on Wednesday, Al Jazeera reported, but communication difficulties meant there was no official account of the strike from the Gaza health ministry. Hussam Abu Safia, the director of Beit Lahiya’s struggling Kamal Adwan hospital, posted a video of patients fleeing from the top floors of the building as it was hit by artillery fire.

Israel cut the territory in two earlier this year by creating what it calls the Netzarim corridor, separating what was once the densely populated Gaza City from the rest of the strip. In Tuesday’s briefing, Cohen also confirmed that northern Gaza has now been split again, to divide Gaza City from the more rural north.

Resettling or permanently reoccupying Gaza is not official Israeli policy, but senior Israeli defence officials recently told the Israeli daily Haaretz that with no other alternatives on the table, the government is aiming to annex large parts of the territory.

Israeli strikes on buildings in Barja, near the Lebanese capital of Beirut, killed at least 30 people. Photograph: Ed Ram/Getty Images

Israel’s new war with the powerful Shia Lebanese group Hezbollah, now in its second month, also shows no sign of slowing or stopping. At least 30 people were killed in an Israeli airstrike on a residential building in Barja, near Beirut, on Tuesday night, with rescue efforts continuing into Wednesday. Many of those killed were women and children, according to Mahmoud Seif al-Dine, a local municipality employee.

“This was a civilian building in a civilian neighbourhood, there were no indications of anything to do with Hezbollah or weapons. We don’t know why they struck, what we saw were women, children and civilians that were killed,” Seif al-Dine said.

Tuesday’s strike was the second hit on Barja, a Sunni town that is hosting about 27,000 people who have been displaced by Israeli bombing in south Lebanon over the past year. The attack was making residents fearful of welcoming displaced people, said Barja’s mayor, Hassan Saad.

Hezbollah shot a volley of rockets at Tel Aviv and other areas in central Israel on Wednesday afternoon, with at least one rocket falling in the Ben Gurion car park without causing injuries. Videos from the scene showed a car impaled by the remains of a Hezbollah rocket.

The new secretary-general of Hezbollah, Naim Qassem, said in a speech on Wednesday that the group had “tens of thousands” of fighters at the ready and that nowhere in Israel was “off limits” for its attacks. He added that Hezbollah is now in a “defensive state” in south Lebanon, indicating that Hezbollah fighters were dug in their positions and that the group was prepared for a war of attrition of Israel.

“We believe that only one thing can stop this aggressive war, which is the battlefield – both on the border and inside Israel,” Qassem said. The group has said it is open to a ceasefire, but that has its own conditions to stop fighting.

Bethan McKernan in Jerusalem and William Christou in Beirut