EU foreign affairs chief Josep Borrell on Saturday called for a probe into deadly shelling that damaged an office of the International Committee of the Red Cross (ICRC) in Gaza.

"The EU condemns the shelling which damaged the ICRC office in Gaza and led to dozens of casualties. An independent investigation is needed and those responsible must be held accountable," Borrell wrote on X.

Meanwhile, days after Israel announced a daily pause in fighting on a key route to allow more aid into Gaza, chaos in the besieged Palestinian territory has left vital supplies piled up and undistributed in the searing summer heat.

More than eight months of war have led to dire humanitarian conditions in the Gaza Strip and repeated UN warnings of famine with outside aid severely restricted.

Desperation among Gaza's 2.4 million population has increased as fighting rages, sparking warnings from aid agencies that they are unable to deliver aid including vegetables.

Israel says it has let supplies in and called on agencies to step up deliveries.

"The breakdown of public order and safety is increasingly endangering humanitarian workers and operations in Gaza," the United Nations Office for the Coordination of Humanitarian Affairs, also known as OCHA, said in a briefing on Friday.

"Alongside the fighting, criminal activities and the risk of theft and robbery has effectively prevented humanitarian access to critical locations."

But Israel says it has allowed hundreds of trucks of aid into southern Gaza, trading blame with the United Nations over why the aid is stacking up.

It shared aerial footage of white and black containers lined up on the Gazan side of the Kerem Shalom crossing and more trucks arriving to add to the stockpile.

With civil order breaking down in the territory, the UN says it has been unable to pick up any supplies from Kerem Shalom since Tuesday, leaving crucial aid in limbo.

A deputy UN spokesman this week said the crossing "is operating with limited functionality, including because of fighting in the area". (AFP)