Twelve of Israel’s most prominent human rights organisations have signed an open letter accusing the country of failing to comply with the international court of justice’s (ICJ) provisional ruling that it should facilitate access of humanitarian aid into Gaza.

The court in The Hague made a number of legal requirements of Israel when it issued a provisional ruling in late January in response to South Africa’s complaint accusing the state of committing genocide in its military campaign in Gaza.

The requirements included taking all measures to prevent intentional harm to civilians, facilitating immediate humanitarian aid to the Gaza Strip, preventing and punishing direct or public incitement to genocide, and preserving evidence of any wrongful acts committed during the country’s war against Hamas.

In their letter, the rights groups say Israel was legally obliged to implement the measures ordered by the court but had so far failed to do so. Signatories to the letter include the military whistleblower group Breaking the Silence and the Association for Civil Rights in Israel.

“The ICJ order is a legal obligation to end the humanitarian catastrophe in Gaza. It must be abided by, not only to ease the urgent suffering of civilians but for the sake of humanity as a whole,” the letter says. It also notes that the ICJ urged Hamas to immediately and unconditionally release all Israeli hostages.

Israel has faced renewed pressure over the lack of humanitarian access to Gaza. The US and other countries have airdropped aid into the coastal strip, and the US and EU have ordered the opening of a sea corridor to the coastal territory.

The letter emerged as the UN secretary general, António Guterres, repeated his call for a truce in the Israel-Hamas war in the Gaza Strip. He asked for the release of hostages held by Hamas and the removal of “all obstacles to ensure the delivery of lifesaving aid at the speed and massive scale required” to Gaza, where the UN has warned that a quarter of the population are on the brink of famine.

On Monday, a Spanish charity ship with food aid prepared to sail from Cyprus to the Gaza Strip. The non-governmental group Open Arms said its boat would tow a barge with 200 tonnes of food, which its partner, the US charity World Central Kitchen, would then unload on Gaza’s shores.

“As members of Israel-based civil society committed to human rights and the rule of law, we condemn the fact that Israel has so far failed to change its behaviour based on the measures imposed by the ICJ, as well as the fact that humanitarian aid to Gaza dropped by 50% in the month following the ruling,” the letter says.

“We call for an immediate ceasefire, which must include the return of the hostages. We urge the Israeli government to comply with the ICJ order and implement the court’s provisional measures, which are essential to mitigating and overcoming the humanitarian catastrophe in Gaza.

“Moreover, we call on the international community to use its collective influence to promote and support an immediate ceasefire and the implementation of the provisional measures, and to increase its efforts to ensure that the Israeli hostages are returned from Gaza.”

Although the UN’s top court did not order a cessation of hostilities, its ruling was seen as a stark warning to Israel about the degree of international legal scrutiny of the months-long military operation it launched in response to the Hamas attacks of 7 October.

The ruling, seen as a sharp rebuke of Israel’s wartime conduct, added to growing international pressure on the country to halt its offensive, which has caused widespread civilian destruction and led to the displacement of upwards of 85% of Gaza’s population of 2.3 million people.

The provisional order was condemned at the time by Israel’s prime minister, Benjamin Netanyahu, who said the fact the court was willing to discuss the genocide allegations was a “mark of shame that will not be erased for generations”.

The international human rights community has also expressed concern about Israel’s failure to abide with the ICJ ruling.

Two weeks ago Amnesty International warned Israel’s “failure” to allow access for humanitarian aid came at a time when the population was on the “brink of famine”.

“Not only has Israel created one of the worst humanitarian crises in the world, but it is also displaying a callous indifference to the fate of Gaza’s population by creating conditions which the ICJ has said places them at imminent risk of genocide,” said Heba Morayef, the regional director for the Middle East and North Africa at Amnesty International.

The latest concerns over the humanitarian situation in Gaza came amid unconfirmed reports in Israeli media of the possible killing of Marwan Issa, the deputy head of Hamas’s military wing in Gaza, in an airstrike in the territory. So far, Israel has been unable to reach the senior leaders of Hamas – one its principal war aims – in Gaza.

Hours later, Israel’s prime minister, Benjamin Netanyahu, said in a video on X that Israel was on the way to total victory and would “reach everyone” in Hamas.