JERUSALEM (AFP) - A text message, a phone call, or an initial strike on the roof. Israel says it gives Gaza civilians warnings to evacuate before bombardment, but activists say it is not nearly enough.

In the besieged coastal enclave of some two million inhabitants, under near-relentless bombardment from the Israeli military for the past 10 days, many are railing against flaws in the "roof knocking" technique.

The campaign on the territory run by Islamist group Hamas has killed at least 230 Palestinians, including 65 children, Gaza health authorities say, and displaced tens of thousands from their homes.

Many bereaved relatives say their family members are being bombed without warning, while others say their telephones have rung, but they were not given enough notice.

This was the case last Saturday (May 15) for Mr Jawad Mehdi, the owner of Jala Tower in Gaza City that was until that day, home to the offices of two foreign media outlets.

Mr Mehdi said an Israeli intelligence officer warned him he had one hour to ensure the building was evacuated, and his plea for "10 extra minutes", broadcast live on television, was denied.

Journalists grabbed equipment and scrambled down the stairs before a missile slammed into the 13-storey building, flattening it.

The Israeli military has been calling residents, sending them text messages, dropping flyers or firing low-yield bombs onto roofs since its war on Gaza in 2008-2009.

During that campaign, the Israeli military said it had made 165,000 phone calls to residents in Gaza instructing them to leave home immediately, often sending pre-recorded messages in Arabic.

The UN humanitarian agency in a 2009 report said that in some cases, the strike occurred only five minutes after the phone call.

More rounds of bombing followed in 2012 and 2014.

The US-led coalition fighting Islamic State group extremists then adopted the technique in Iraq in 2016.

In the Jabaliya camp in the north of the Gaza Strip on Thursday morning, Mr Mohammed al-Ashqar said he had been warned to run out of his home.

"We received last night a call to evacuate the place, and when we did, the entire neighbourhood was destroyed," he told AFP. "My shop and house were completely destroyed."

But it is unclear how often the Israeli military has tried to give such prior notice in the latest Gaza conflict.

An air force officer, who spoke on condition of anonymity, said 1,000 strikes had hit the enclave, but a warning had not been issued in all cases.

"When it's infrastructure, we can use this technique, but not if eliminating terrorists," he said.

"We fire a small, empty missile to knock on the roof and make the civilians understand they must leave," he told AFP. "As soon as we have the most assurances possible that the building has been evacuated, we fire."

He said these shots were both to avoid "collateral damage", and to protect Israel after the chief prosecutor of the International Criminal Court in March said she had opened a probe into the situation in the Israeli-occupied territories.

That investigation, which infuriated Israel, will mainly focus on the 2014 Gaza war.

He said the Israeli general prosecutor was involved in laying out protocols for these so-called warning strikes.

Days earlier, Mr Mohammad al-Hadidi cradled his wounded baby boy Omar, the only surviving child after air strikes killed his wife and four other sons last Friday night.

He asked what they had done "to deserve being bombed without any warning to evacuate the home".

In that case, Israel claimed it had fired at "terrorists".

Rights group Amnesty International slammed the practice as not nearly enough to warn civilians or protect them.

"Giving warning does not absolve an attacking force from the obligation to adhere to other rules of international humanitarian law", including not targeting civilians, regional spokesman Sara Hashash said.

"In many cases key elements of effective warning have been missing, including timelines, informing civilians where it is safe to flee, and providing safe passage and sufficient time to flee before an attack," she said.

Ms Hashash said the warning strikes themselves could also be lethal.

"Amnesty International has documented cases of civilians killed or injured by such missiles in previous Israeli military operations," she said.