The United States has allowed Israel, waging an offensive in the Gaza Strip, to tap a local US arms stockpile in the past week to resupply it with grenades and mortar rounds, Rear Admiral John Kirby, the Pentagon's press secretary, has said.

The munitions were located inside Israel as part of a programme managed by the US military and called War Reserves Stock Allies-Israel (WRSA-I), which stores munitions locally for US use that Israel can also access in emergency situations.

Israel, however, did not cite an emergency when it made its latest request about 10 days ago, a defence official said on Wednesday, speaking on condition of anonymity.

On Sunday, Barack Obama, the US president, called for an immediate and sustainable ceasefire in Gaza.

Washington allowed Israel to access the strategic stockpile to resupply itself with 40mm grenades and 120mm mortar rounds to deplete older stocks that would eventually need to be refreshed.

In a statement, Kirby said: "Both munitions had been in WRSA-I stock for a few years, well before the current crisis.

"All stocks in WRSA-I, as required by law, are 'in excess to US requirements'.

"Issuing munitions from the WRSA-I stockpile was strictly a sourcing decision and White House approval was not required.

"The United States is committed to the security of Israel, and it is vital to US national interests to assist Israel to develop and maintain a strong and ready self-defence capability.

"This defence sale is consistent with those objectives."

Additional Israeli requests for US-manufactured ammunition were also being processed in the US, the anonymous defence official said.