The UN human rights office has said it received "disturbing information" alleging the Israeli army summarily executed at least 11 unarmed Palestinians.
The victims, all men, were alleged to have been killed in front of family members in Gaza City's Rimal neighbourhood, with the UN rights office saying it "raises alarm about the possible commission of a war crime".
The Israeli military allegedly surrounded and raided a building in Rimal where four families were sheltering on Tuesday between 20:00 and 23:00 local time (18:00 and 21:00 GMT)
"According to witness accounts circulated by media sources and Euro-Med Human Rights Monitor, while in control of the building and the civilians sheltering there, the IDF [army] allegedly separated the men from the women and children, and then shot and killed at least 11 of the men, mostly aged in their late 20s and early 30s, in front of their family members," the UN rights office said.
The United Nations agency, also known as the Office of the High Commissioner for Human Rights (OHCHR), added that the military allegedly then ordered women and children into a room and "either shot at them or threw a grenade into the room, reportedly seriously injuring some of them, including an infant and a child".
OHCHR said it had verified the killings at the building, but the details and circumstances remained "under verification".
"The Israeli authorities must immediately institute an independent, thorough, and effective investigation into these allegations, and if found to be substantiated, those responsible must be brought to justice and measures implemented to prevent any such serious violations from recurring," the UN rights office said.
The International Centre of Justice for Palestinians (ICJP) said in a press release that "more reports emerge" each day showing "overwhelming evidence of war crimes" being carried out by the Israeli army.
The ICJP said it calls on the International Criminal Court to "act swiftly" to "maintain its legitimacy and credibility".
ICJP director Tayab Ali said: "The strength and credibility of evidence that the Israel Defence Forces (IDF) are engaged in war crimes has become overwhelming.
"The world can see and hear testimony directly from eyewitnesses in Gaza on their television screens leaving them in little doubt about the allegations."
Ali called on the US, UK, and international community to "immediately halt their support and facilitation of war crimes".
It comes after the bodies of more than a dozen Palestinians reportedly shot dead by Israeli forces were found at a school in the al-Faluja area in northern Gaza last week.
Eyewitnesses and relatives of the victims said they were shot at point-blank by Israel's troops. The victims were reportedly killed overnight Tuesday-Wednesday, but this could not be confirmed.
Distressing footage of the bodies was obtained by pan-Arab broadcaster Al Jazeera and shared on social media.