Israeli forces have seized control of Gaza’s Rafah border crossing, cutting off a vital route for humanitarian aid and potential sanctuary for civilians from a building offensive.

The Israeli military said on Tuesday that it had seized “operational control” of the Gaza side of the border post, which links the besieged enclave with Egypt. The closure of the crucial passage and positioning of tanks in the centre of Rafah is seen as a demonstration of Israel’s determination to press on with an assault on the southern city despite ongoing truce talks.

The 401st Brigade entered the Rafah crossing early on Tuesday, the Israeli military said, closing a route vital for the aid entering Gaza and any civilians able to flee the fighting to Egypt.

The military claimed that the crossing was “being used for terrorist purposes”, alleging that Hamas’s mortar attack on Sunday on the Karem Abu Salem crossing, known as Kerem Shalom to Israelis, which remains closed, was launched from the vicinity. However, it has not so far provided evidence.

The operation came amid an overnight assault on eastern parts of the city. Warplanes pounded residential homes, killing at least 12 people.

Israel’s military said in a statement it had struck numerous Hamas targets in eastern Rafah, killing about 20 fighters.

A spokesman for the Palestinian Crossings Authority acknowledged to The Associated Press news agency that Israeli forces had seized the crossing and closed it for the time being.

“It’s been a very difficult night,” reported Al Jazeera’s Hani Mahmoud from Rafah. “It’s been very violent, very bloody and full of destruction.”

The assault comes despite Hamas having said on Monday that it had agreed with the terms of a truce deal hammered out by mediators.

However, pressed by hardline nationalist coalition partners who have demanded a full offensive on Rafah, Israeli Prime Minister Benjamin Netanyahu appears set to press on regardless.

Tareq Abu Azzoum reported from Rafah that the Israeli military carried out an incursion on the eastern side of Rafah, during which there was a heavy exchange of fire with Hamas fighters amid an intense bombing campaign, with the main objective of seizing control of the crossing.

The Israeli control of the border post “is devastating because … Palestinians will no longer be able to leave the territory”, he said.

Despite urgent warnings from its closest allies that an offensive on the city risks huge numbers of civilian casualties, Israel insists that its plans will allow it to clear Rafah and press on to attack the Hamas command and fighters there.

“The Rafah offensive has started again, in spite of all the requests of the international community, the US, the European Union member states, everybody asking Netanyahu not to attack,” Josep Borrell, the EU’s top diplomat, told journalists on Tuesday. “I am afraid that this is going to cause again a lot of casualties, civilian casualties. Whatever they say,” he said, adding, “there are no safe zones in Gaza.”

Israeli forces whipped up panic on Monday as they ordered 1.4 million or so Palestinians in Rafah – most of whom are displaced following previous instructions from the Israeli military – to evacuate.

The Israeli army reiterated on Tuesday that it has “encouraged” displaced people and international humanitarian organisations operating in eastern Rafah to “temporarily evacuate”.

However, people sheltering in Rafah, amid poor conditions with little shelter, food, or medicine, have few places to go.

The closure of the border crossing only threatens to worsen those shortages and trap more people close to the fighting.

Sources from three humanitarian relief agencies told the Reuters news agency that aid shipments had been halted due to the closure of the crossing.

The latest Israeli operation sees them being pushed towards al-Mawasi on the coast, where the military says it has set up field hospitals, tents, and medical supplies.

“The Israeli military is … strategically cutting off the Gaza Strip and sealing it off from the region,” suggested Al Jazeera’s Mahmoud.

“With the Israeli military presence there right now, we can safely say that we’re looking at a very difficult situation in terms of getting humanitarian aid into Gaza,” he said.

“At the same time, when we look at the location of the Rafah crossing, at almost the centre of the city, that indicates that we’re very close to a full invasion of Rafah.”