At least 27 people were killed by Israeli fire as they waited for food at a distribution point set up by an Israeli-backed foundation in Gaza, according to health officials in the strip.

It is the third such incident in three days, with Israel admitting for the first time during the recent events that its forces shot at individuals who were moving towards them.

The Gaza civil defence spokesperson Mahmoud Bassal told Agence France-Presse: “Israeli forces opened fire with tanks and drones on thousands of civilians who had gathered since dawn near the al-Alam roundabout in the al-Mawasi area, north-west of Rafah.”

Gaza’s health ministry said 27 people were killed early on Tuesday. Hamas-affiliated media also carried the reports.

“There were three children and two women among the dead,” Mohammed Saqr, the head of nursing at Nasser hospital, which received the 27 bodies, told the Guardian. “Most of the patients had gunshot wounds, others had shrapnel all over the bodies, which means they were targeted with tanks or artillery munitions.”

Hisham Mhanna, a spokesperson for the International Committee of the Red Cross, confirmed its field hospital in Rafah had received 184 wounded people, 19 of whom were declared dead on arrival. Eight more later died from their wounds.

A video circulating on social media documented the arrival of injured people at the Red Cross hospital from a food distribution point in Gaza’s Rafah governorate. It showed dead bodies and the injured being dragged by people inside the health facility.

In a statement, the Israel Defense Forces (IDF) said troops fired shots near a food distribution complex after noticing “a number of suspects moving towards them”.

“The forces fired evasive shots, and after they did not move away, additional shots were fired near the individual suspects who were advancing towards the forces.

“The individuals were moving towards forces in a way that posed a threat to them,” the military said, without specifying who the suspects were.

The IDF said the incident was under investigation, adding that its forces “are not preventing Gaza residents from reaching the aid distribution sites. The shooting was carried out about half a kilometre from the distribution site.”

The Gaza Humanitarian Foundation (GHF), an Israeli-backed organisation that has taken over distribution of food in Gaza, acknowledged that the Israeli military was investigating whether civilians were wounded “after moving beyond the designated safe corridor and into a closed military zone” in an area that was “well beyond our secure distribution site”.

Yasser Abu Lubda, a 50-year-old displaced Palestinian from Rafah, told Associated Press the shooting started at around 4am in the city’s Flag Roundabout area, about 1km (0.6 miles) away from the food distribution hub. He said he saw several people killed or wounded.

Neima al-Aaraj, a woman from Khan Younis, gave a similar account. “There were many martyrs and wounded,” she said, adding that the shooting by Israeli forces was “indiscriminate”.

She said she managed to reach the hub but returned empty-handed. “There was no aid there,” she said. “After the martyrs and wounded, I won’t return. Either way we will die.”

Rasha al-Nahal, another witness, said “there was gunfire from all directions”. She said she counted more than a dozen dead and several wounded along the road. She said she also found no food when she arrived at the distribution hub, and that Israeli forces “fired at us as we were returning”.

The United Nations’ human rights chief, Volker Türk, described the “deadly attacks” on civilians around food distribution as “a war crime”.

“Deadly attacks on distraught civilians trying to access the paltry amounts of food aid in Gaza are unconscionable,” Türk said. “Attacks directed against civilians constitute a grave breach of international law and a war crime.”

Speaking before Tuesday’s incident, the UN secretary general, António Guterres, called for an independent investigation into Sunday’s killings. “I am appalled by the reports of Palestinians killed and injured while seeking aid in Gaza yesterday,” he said on Monday.

“I call for an immediate and independent investigation into these events and for perpetrators to be held accountable.”

The reported shooting follows similar incidents this week of Palestinians being killed and injured by Israeli fire as they sought food at newly established distribution points.

Last Wednesday, Hamas accused Israel of killing at least three Palestinians and wounding 46 near one of the GHF distribution sites, an accusation the group denied. The Israeli military said its troops fired warning shots in the area outside the compound to re-establish control as thousands of Palestinians rushed to the site.

More than 30 Palestinians were killed by Israeli fire on Sunday as they went to receive food at a GHF distribution point, according to witnesses. A hospital run by the Red Cross confirmed it treated many wounded.

The Israeli forces denied “firing at civilians” in Sunday’s incident. However, an IDF official admitted that Israeli soldiers fired “warning shots toward several suspects who advanced toward the troops”, near the aid distribution site, without specifying who the suspects were.

Reuters footage showed ambulance vehicles carrying injured people to Nasser hospital on Sunday. Other clips emerged showing people running and ducking, with apparent gunfire audible in the background. One seems to have been filmed in the Salah al-Din road, south of a distribution site in the Netzarim corridor.

Speaking before Tuesday’s incident, the UN secretary general, António Guterres, called for an independent investigation into Sunday’s killings. “I am appalled by the reports of Palestinians killed and injured while seeking aid in Gaza yesterday,” he said on Monday.

“I call for an immediate and independent investigation into these events and for perpetrators to be held accountable.”

Israel imposed a blockade on all supplies in March, saying Hamas was seizing deliveries for its fighters, which the group denies. Earlier this month, a global hunger monitor said half a million people in the strip faced starvation.

The IPC estimated that nearly 71,000 children under the age of five were expected to be “acutely malnourished”, with 14,100 cases expected to be severe in the next 11 months.

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The GHF took over the handling of aid despite objections from the UN. The desperately needed supplies started flowing on a day that Israeli strikes killed at least 52 people in Gaza. The organisation is made up of former humanitarian, government and military officials.

Last week, the GHF’s head, Jake Wood, resigned, saying it had become clear the foundation would not be allowed to operate independently.

The UN and other humanitarian organisations rejected the new system for food distribution, saying it would not be able to meet the needs of Gaza’s 2.3 million people and allowed Israel to use food as a weapon to control the population.

• The Associated Press, Reuters and Agence France-Presse contributed to this report.