(AFP) - Israeli ground troops fighting to destroy Hamas had surrounded Gaza City on Friday as top US diplomat Antony Blinken arrived in Israel for a trip focused on "concrete steps" to minimise Palestinian civilian casualties.

Separately, Israel began expelling thousands of Palestinian workers back to Gaza, despite ongoing fighting and air strikes that have killed thousands of civilians in the territory.

And in Geneva, the United Nations launched an emergency aid appeal seeking $1.2 billion to help some 2.7 million people facing a humanitarian crisis in Gaza and the West Bank.

The leader of Lebanon's Iranian-backed Hezbollah, Hassan Nasrallah, was to make a speech later in the day, breaking with weeks of silence, amid concerns of a broader regional conflagration.

Ahead of Blinken's arrival, Israel's military said it had "completed the encirclement" of Gaza's largest city -- signalling a new phase in the nearly month-long conflict.

Fighting was triggered by Hamas' bloody raids on October 7, which Israeli officials say killed more than 1,400 people.

The health ministry in Hamas-run Gaza says more than 9,000 people have died in Israeli bombardments, mostly women and children.

After the Hamas assault, Israeli forces moved to re-establish security on the border, trapping thousands of Palestinian workers inside Israel.

On Friday, officials began to force them back into Gaza, AFP journalists at the Karem Abu Salem crossing saw.

"Thousands of workers who were blocked in Israel since October 7 have been brought back," Hisham Adwan, head of Gaza's crossings authority, told AFP.

- Workers expelled -

Israel said late on Thursday it would start sending the workers back to Gaza.

"Israel is severing all contact with Gaza. There will be no more Palestinian workers from Gaza," the Israeli security cabinet said in a statement.

The United Nations Human Rights Office said it was "deeply concerned" about the expulsions.

"They are being sent back, we don't know exactly to where," and whether they "even have a home to go to", spokeswoman Elizabeth Throssell told a news conference in Geneva.

Before the war started, some 18,500 Gazans were holding Israeli work permits, according to figures provided by COGAT, the Israeli defence body responsible for Palestinian civilian affairs. COGAT would not immediately say how many of those Gazans were working inside Israel on October 7.

New Israeli strikes rocked the Gaza Strip on Friday morning, an AFP correspondent said, and the Gaza health ministry reported at least 15 deaths in Gaza City's Zeitun neighbourhood and seven in Jabalia refugee camp.

The Hamas government has said 195 people were killed in Israeli bombardments on Jabalia earlier this week, with hundreds more missing and wounded, figures AFP could not independently verify.

Before his departure, Blinken said he would seek to ensure that harm to Palestinian civilians is reduced, in a visible shift of tone for the United States which has promised full support and ramped-up military aid to Israel.

"We will be talking about concrete steps that can and should be taken to minimise harm to men, women and children in Gaza," Blinken said.

"This is something that the United States is committed to."

Prime Minister Benjamin Netanyahu said Israel had already had some "very impressive successes" with troops "more than on the outskirts of Gaza City. We are advancing," he said late Thursday at a base near Tel Aviv.

Israel's military describes Gaza City as "the centre of the Hamas terror organisation".

Although many of the city's half-a-million residents fled south following Israel's warning to leave ahead of a ground operation, those who stayed behind have endured weeks of aerial bombardment, dwindling supplies and daily carnage.

- 'Curse of history' -

But yet more mayhem seems to lie ahead, as the conflict turns to urban and underground warfare -- with Hamas fighting from a tunnel complex believed to span hundreds of kilometres (miles).

The Ezzedine al-Qassam Brigades, the military wing of Hamas, insisted Israeli soldiers would go home "in black bags".

"Gaza will be the curse of history for Israel," spokesman Abu Obeida said.

Israel's allies have backed its right to self-defence, but there is growing global concern and anger at how Israel has chosen to prosecute the war.

A group of UN-mandated human rights experts -- who do not speak for the United Nations -- warned Thursday that "time is running out to prevent genocide and humanitarian catastrophe in Gaza".

Israel's Geneva embassy denounced the report as Hamas "propaganda" in a social media post.

On Friday, the UN Office for the Coordination of Humanitarian Affairs (OCHA) said the cost of meeting the needs of the 2,7 million people living in Gaza and the Israeli-occupied West Bank had risen to $1.2 billion, and launched an appeal for donors.

Both Israel and the United States have ruled out a blanket ceasefire, which they say would allow Hamas to regroup and resupply.

US President Joe Biden has backed "temporary, localised" pauses in fighting to allow humanitarian work to be done.

- Escape to safety -

Countries around the world recalled their ambassadors from Israel in protest at the strikes. Bolivia severed diplomatic ties.

Israel has sought to show Jabalia was a legitimate target, saying it killed a senior Hamas commander in a tunnel complex below the camp.

On Thursday some 400 more foreigners and dual nationals managed to escape the war to Egypt, along with 60 wounded Palestinians.

Egypt has said it would help evacuate 7,000 foreigners through Rafah, which was to open again on Friday, a source at the crossing told AFP.

The UN said more than 100 trucks with aid crossed into Gaza on Thursday, a significant increase from previous days.

A total of 374 trucks have entered since a US-brokered deal was enacted on October 21, far short of what aid agencies say is needed.

© Agence France-Presse