Benjamin Netanyahu has said he has given orders to the Israeli army to seize control of 70% of the Gaza Strip in a move that threatens to torpedo an already fragile ceasefire and create catastrophic humanitarian conditions in the already devastated territory.

Under the US-brokered ceasefire in October, the Israeli army withdrew to a demarcation line which gave Israel direct control of 53% of the occupied territory. Since then, Israeli forces have steadily advanced their positions westward into the Hamas-controlled half of the strip, and declared an ever-expanded no man’s land west of that, within which they claim the right to decide who can enter and open fire on anyone perceived as a threat.

In recent days, Israeli-backed armed militias have taken a leading role in emptying the territory along the ceasefire line, telling residents to vacate their homes or shelters.

Throughout the eight months of the ceasefire, Israeli forces have continued to open fire on Palestinians within range of the “yellow line” splitting the strip, and carry out airstrikes deeper inside western Gaza, killing more than 900 Palestinians since the truce began.

Speaking at a conference in an occupied West Bank settlement, Netanyahu, who is struggling for his political survival before elections in the next few months, spelled out the extent of Israel’s territorial goals.

The Israeli prime minister said: “We are currently squeezing Hamas. We now control 60% of the territory in the strip. You know, we were at 50, we moved to 60. My directive is to move to … 70%.”

The defence minister, Israel Katz, said on Wednesday that the government’s ultimate aim was for large numbers of Palestinians to leave Gaza by what he called “voluntary migration” but what human rights activists describe as a long-term plan for ethnic cleansing by making living conditions inside Gaza intolerable.

The expansion of Israeli military control would be a direct violation of the October ceasefire, the UN security council resolution that endorsed it, and Donald Trump’s 20-point peace plan, which laid out a temporary “yellow line” splitting Gaza into Israeli- and Hamas-run halves pending further peace negotiations.

The Trump plan also said: “No one will be forced to leave Gaza, and those who wish to leave will be free to do so and free to return. We will encourage people to stay and offer them the opportunity to build a better Gaza.”

Muhammad Shehada, a visiting fellow at the European Council on Foreign Relations, said: “Netanyahu is now declaring the whole Trump deal, the framework for Gaza, to be null and void. That’s what it means in a nutshell. There’s no other way to spell it out.”

Israeli forces have systematically destroyed the remaining buildings in their zone, so its expansion to 70% of Gaza would mean that the 2.2 million Palestinians who have survived the war would be crammed into less than a third of their original territory, which was already overcrowded.

“The conditions there are already appalling. It is the single most overcrowded place on the face of the planet,” Shehada said. “Every square metre has another displaced family, another makeshift tent, or some sort of improvised shelter on it. So it would be a death sentence for a lot of people who physically have no place to go.”

An Israeli army spokesperson referred a request for comment on Netanyahu’s 70% threat “to the political echelon”.

Israeli forces have been steadily expanding their area of control over the course of the ceasefire. A UN briefing on Sunday for the heads of humanitarian agencies working in Gaza recorded some of the most recent encroachment.

In the northern district of Jabalia, for example, the UN presentation, which has been seen by the Guardian, said: “Tanks advancement [were] reported on a daily basis – drones targeting any movement close [to] the yellow line.”

Israeli tanks were also reported advancing east of the southern city of Khan Younis.

The UN briefing refers to an Israeli-backed anti-Hamas militia run by a Gaza warlord, Ashraf al-Mansi, saying it had advanced westwards from the yellow line around Jabalia last week.

Such militias have been increasingly active along the yellow line, apparently functioning as shock troops for the Israeli army, carrying out attacks on Hamas but also telling Palestinian residents near the yellow line to leave their homes.

Wael Nayef Abu al-Ajeen, a 26-year-old who lives to the east of Deir al-Balah in southern Gaza, said his family had been forced out by militiamen earlier this month.

“It was at around 1pm when armed men affiliated with the militias entered our area. They went to the homes of the Abu al-Ajeen family there and informed them that they had until 10pm to evacuate all the houses in the area,” Ajeen said. “They instructed them to take whatever furniture and belongings they could carry and to empty the houses as much as possible. They also told them not to return until they were contacted and informed that it was permitted.

“As a result, everyone panicked, and people gradually began leaving and moving their furniture and whatever belongings they could carry until the area was almost completely emptied.”

Nasser Khdour, a researcher at monitoring group the Armed Conflict Location and Event Data Project said: “We have seen that the militias are not only attacking Hamas, but also they are contributing to pushing the residents who are living close to their line, further to the west.

“We have seen killing, arresting and kidnapping of civilians living in these areas, and recently, there’s an increase also in the militias’ patrolling activities.”

A UN security council resolution passed in November, delegated the monitoring of the ceasefire to a Trump-appointed Board of Peace, which named a Bulgarian UN veteran diplomat, Nickolay Mladenov, as “high representative in Gaza”.

Mladenov was widely criticised for his report to the security council last week, which assigned primary blame for the failings of the ceasefire on Hamas, accusing it of refusing to disarm, without holding Israel accountable for its violations. Hamas has signalled it is ready to discuss disarmament once Israel has fulfilled its obligations under the first phase of the ceasefire, in particular by ceasing the bombardment of Gaza and withdrawing to the original yellow line.

Gershon Baskin, an Israeli analyst who has taken part in several Israeli-Palestinian backchannel negotiations, said he believed the original ceasefire plan had collapsed.

He said: “My understanding is that the negotiations with Hamas are over. The Americans gave Hamas the offer on a plan for disarmament, which took into account all the things that Hamas demanded already two months ago, but Hamas didn’t respond”

Baskin said he believed the US would now switch to a fallback plan aimed at carrying out reconstruction work in the Israeli-run “green” zone, and only allowing Palestinians to move there from the Hamas-run “yellow” zone, who had been vetted for links to Hamas or other radical groups.

Baskin said: “At the end of the day, the only people remaining in the yellow zone, according to the Americans, are Hamas and other armed groups. And then Israel will be free to deal with them as they want. This is the thinking, this is the planning, and this is what I see happening in the coming weeks and months.”