The Biden administration paused the shipment of thousands of bombs to Israel last week because of its concerns about an Israeli invasion of Rafah, the last remaining Hamas stronghold in the Gaza Strip.

The shipment was meant to transfer 3,500 bombs to Israel, which the United States halted over worries about the large munitions in the package being used in an urban setting, an anonymous administration official told the Associated Press. The package included 1,800 2,000-pound bombs and 1,700 500-pound bombs, according to the AP.

The pause marks the first time the U.S. has publicly held up military aid to Israel since the October 7 Hamas attack. An American official described the decision to the Washington Post as a “shot across the bow” to signal the Biden administration’s unease with a Rafah operation.

Despite the alleged concerns, Axios reported Tuesday that Israel had not crossed a “red line” from the administration’s perspective with its ongoing limited engagement in Rafah, which began Monday after Israel evacuated civilians from four neighborhoods in the eastern part of the city. Biden reiterated his “iron clad” support for Israel “even when we disagree,” during a Tuesday speech on antisemitism.

However, Biden indicated in a Monday conversation with Israeli prime minister Benjamin Netanyahu that the U.S. would not support a major ground operation in Rafah, with national security adviser Jake Sullivan saying recently that the nature of Israel’s engagement in Rafah will impact the U.S.’s posture toward the broader war.

The decision to pause the arms shipment comes as the Biden administration is expected to issue a statement on whether Israeli airstrikes and restrictions on aid to Gaza have violated U.S. and international law, a review the White House agreed to in February after pressure from some Senate Democrats. State Department spokesman Matthew Miller told reporters on Tuesday that the Biden administration hopes to have its review completed by Wednesday, though it may take until the end of the week.

Biden described Israel’s airstrikes as “indiscriminate” in December, and he signaled that he may be open to cutting military aid after Israel accidentally killed seven aid workers from the World Central Kitchen in April.