The Biden administration has told key lawmakers it will send more than $1 billion ($1.6 billion) in additional arms and ammunition to Israel, three congressional aides said on Tuesday. But it was not immediately known how soon the weapons would be delivered.

It’s the first arms shipment to Israel to be revealed since the administration put another arms transfer, consisting of 3500 bombs of up to 2000 pounds each, on hold this month. The Biden administration, citing concern for civilian casualties in Gaza, has said it paused that bomb transfer to keep Israel from using those particular munitions in its offensive in the crowded southern Gaza city of Rafah.

The package disclosed on Tuesday includes about US$700 million ($1.1b) for tank ammunition, US$500m ($825m) in tactical vehicles and US$60m ($99m) in mortar rounds, the congressional aides said. They spoke on condition of anonymity to discuss an arms transfer that has not yet been made public.

An Israeli mobile artillery unit fires a shell from southern Israel towards the Gaza Strip, in a position near the Israel-Palestine border. Photo / AP

There was no immediate indication when the arms would be sent. Two congressional aides said the shipment is not part of the long-delayed foreign aid package Congress passed and Biden signed last month. It wasn’t known if the shipment was the latest tranche from an existing arms sale or something new.

The Biden administration has come under criticism from both sides of the political spectrum over its military support for Israel’s now seven-month-long war against Hamas in Gaza - at a time when Biden is battling for re-election against former US president Donald Trump.

Some of Biden’s fellow Democrats have pushed him to limit transfers of offensive weapons to Israel to pressure the US ally to do more to protect Palestinian civilians. Protests on college campuses around the US have driven home the message this spring.

Republican lawmakers have seized on the administration’s pause on the bomb transfers, saying any lessening of US support for Israel - its closest ally in the Middle East - weakens that country as it fights Hamas and other Iran-backed groups. In the House, they are planning to advance a bill this week to mandate the delivery of offensive weaponry for Israel.

Despite the one-time suspension of a bomb shipment, Biden and administration officials have made clear they will continue other weapons deliveries and overall military support to Israel, which is the largest recipient of US military aid.

Biden will see to it that “Israel has all of the military means it needs to defend itself against all of its enemies, including Hamas”, national security spokesman John Kirby told reporters on Monday. “For him, this is very straightforward: He’s going to continue to provide Israel with all of the capabilities it needs, but he does not want certain categories of American weapons used in a particular type of operation in a particular place. And again, he has been clear and consistent with that.”

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The Wall Street Journal first reported the plans for the $1b weapons package to Israel.

In response to House Republicans’ plan to move forward with a bill to mandate the delivery of offensive weapons for Israel, the White House said on Tuesday Biden would veto the bill if it were to pass Congress.

The bill has practically no chance in the Democratic-controlled Senate. But House Democrats are somewhat divided on the issue, and roughly two dozen have signed a letter to the Biden administration saying they were “deeply concerned about the message” sent by pausing the bomb shipment.

One of the letter’s signers, New York representative Ritchie Torres, said he would likely vote for the bill, despite the White House’s opposition.

“I have a general rule of supporting pro-Israel legislation unless it includes a poison pill - like cuts to domestic policy,” he said.

Palestinians mourn relatives killed in the Israeli bombardment of the Gaza Strip at a hospital in Rafah. Photo / AP

In addition to the written veto threat, the White House has been in touch with various lawmakers and congressional aides about the legislation, according to an administration official.

“We strongly, strongly oppose attempts to constrain the president’s ability to deploy US security assistance consistent with US foreign policy and national security objectives,” White House press secretary Karine Jean-Pierre said this week, adding that the administration plans to spend “every last cent” appropriated by Congress in the national security supplemental package signed into law by Biden last month.