(The Hill) — The Biden administration halted a shipment of ammunition bound for Israel last week, Axios first reported, as pressure rises over the Israeli military’s promised invasion of Rafah in Gaza.

Israeli officials were left scrambling as to why the shipment was withheld, Axios reported, while  CNN reported that the decision was unrelated to U.S. opposition to an invasion of Rafah.

The Biden administration has committed to strongly backing Israel in its war against Hamas, signing $26 billion in military and humanitarian aid for the war last week, but officials have repeatedly warned against moving into Rafah, where over a million displaced Palestinians are sheltering from the war.

The National Security Council said in a statement to The Hill that the Biden administration’s backing of Israel has not changed.

“The United States has surged billions of dollars in security assistance to Israel since the October 7 attacks, passed the largest ever supplemental appropriation for emergency assistance to Israel, led an unprecedented coalition to defend Israel against Iranian attacks, and will continue to do what is necessary to ensure Israel can defend itself from the threats it faces,” a NSC spokesperson said.

The move also raises pressure on ongoing cease-fire and hostage negotiations between Israel and Hamas, as rifts between the two sides widen following progress in talks earlier this week.  William Burns attended negotiations Saturday in Cairo, and will remain in the Middle East to work towards a diplomatic solution in the coming days.

A Rafah invasion hangs over the conflict, with Israeli leaders saying a ground attack against the city is inevitable, while the U.N. warns such an attack could have catastrophic civilian casualties. The Biden administration has repeatedly urged Israel not to attack Rafah without a clear plan to avoid civilian losses.

On Sunday, Prime Minister Benjamin Netanyahu signaled that a Rafah invasion is likely, with or without a diplomatic agreement with Hamas or U.S. backing.

“In the terrible Holocaust, there were great world leaders who stood by idly; therefore, the first lesson of the Holocaust is: If we do not defend ourselves, nobody will defend us. And if we need to stand alone, we will stand alone,” he said.

Biden is also facing criticism from Democrats who have pushed him to garner assurances that U.S.-manufactured munitions are being used in accordance with international law. 

Federal law requires that military aid be used lawfully, though an increasing number of Democratic lawmakers have pushed Biden to draw a stronger line on the issue, especially after the State Department determined last week that certain units of the Israeli military were involved in gross violations of human rights.