Pres­i­dent Joe Biden is­sued a stark warn­ing to Is­raeli Prime Min­is­ter Ben­jamin Ne­tanyahu on Thurs­day that fu­ture U.S. sup­port for Is­rael’s Gaza war de­pends on the swift im­ple­men­ta­tion of new steps to pro­tect civil­ians and aid work­ers.

Biden and Ne­tanyahu ‘s rough­ly 30-minute call just days af­ter Is­raeli airstrikes killed sev­en food aid work­ers in Gaza added a new lay­er of com­pli­ca­tion to the lead­ers’ in­creas­ing­ly strained re­la­tion­ship. Biden’s mes­sage marks a sharp change in his ad­min­is­tra­tion’s stead­fast sup­port for Is­rael’s war ef­forts, with the U.S. leader for the first time threat­en­ing to re­think his back­ing if Is­rael doesn’t change its tac­tics and al­low much more hu­man­i­tar­i­an aid in­to Gaza.

The White House would not spec­i­fy what could change about U.S. pol­i­cy, but it could in­clude al­ter­ing mil­i­tary sales to Is­rael and Amer­i­ca’s diplo­mat­ic back­up on the world stage. Ad­min­is­tra­tion of­fi­cials said they ex­pect­ed the Is­raelis to make an­nounce­ments on next steps with­in hours or days and that the U.S. would then as­sess whether the Is­raeli moves go far enough.

Biden “made clear the need for Is­rael to an­nounce and im­ple­ment a se­ries of spe­cif­ic, con­crete, and mea­sur­able steps to ad­dress civil­ian harm, hu­man­i­tar­i­an suf­fer­ing, and the safe­ty of aid work­ers,” the White House said in a state­ment fol­low­ing the lead­ers’ call. “He made clear that U.S. pol­i­cy with re­spect to Gaza will be de­ter­mined by our as­sess­ment of Is­rael’s im­me­di­ate ac­tion on these steps.”

Biden al­so told Ne­tanyahu that an “im­me­di­ate cease-fire is es­sen­tial” and urged Is­rael to reach such an ac­cord “with­out de­lay,” ac­cord­ing to the White House, which de­scribed the con­ver­sa­tion as “di­rect” and “hon­est.”

There was no im­me­di­ate re­ac­tion to the call from the Is­raeli gov­ern­ment.

The lead­ers’ con­ver­sa­tion comes as the World Cen­tral Kitchen, found­ed by restau­ran­teur José An­drés to pro­vide im­me­di­ate food re­lief to dis­as­ter-strick­en ar­eas, called for an in­de­pen­dent in­ves­ti­ga­tion in­to the Is­raeli strikes that killed the group’s staff mem­bers, in­clud­ing an Amer­i­can cit­i­zen.

The White House has said the U.S. has no plans to con­duct its own in­ves­ti­ga­tion even as it called on Is­rael to do more to pre­vent the harm­ing of in­no­cent civil­ians and aid work­ers as it car­ries out its op­er­a­tions in Gaza.

Sep­a­rate­ly, Sec­re­tary of State Antony Blinken told re­porters in Brus­sels that U.S. sup­port would be cur­tailed if Is­rael doesn’t make sig­nif­i­cant ad­just­ments to how it’s car­ry­ing out the war. “If we don’t see the changes that we need to see, there will be changes in our pol­i­cy,” he said.

White House na­tion­al se­cu­ri­ty spokesman John Kir­by echoed the call for “tan­gi­ble” and “con­crete” changes to be tak­en by the Is­raelis be­yond re­it­er­at­ing long stat­ed calls for al­low­ing ad­di­tion­al aid to get in­to Gaza.

“If there’s no changes to their pol­i­cy in their ap­proach­es, then there’s go­ing to have to be changes to ours,” Kir­by said. “There are things that need to be done. There are too many civil­ians be­ing killed.”

The de­mands for Is­rael to bring the con­flict to a swift close were in­creas­ing across the po­lit­i­cal spec­trum, with for­mer Pres­i­dent Don­ald Trump, the Re­pub­li­cans’ pre­sump­tive nom­i­nee to face Biden this fall, say­ing Thurs­day that Is­rael was “ab­solute­ly los­ing the PR war” and call­ing for a res­o­lu­tion to the blood­shed.

“Get it over with and let’s get back to peace and stop killing peo­ple. And that’s a very sim­ple state­ment,” Trump told con­ser­v­a­tive ra­dio host Hugh He­witt. “They have to get it done. Get it over with and get it over with fast be­cause we have to — you have to get back to nor­mal­cy and peace.”

Biden and Ne­tanyahu al­so dis­cussed Iran­ian threats against Is­rael, Kir­by said. Ear­li­er this week, Iran­ian lead­ers vowed to hit back af­ter an airstrike wide­ly blamed on Is­rael de­stroyed Iran’s Con­sulate in Syr­ia, killing 12 peo­ple, in­clud­ing two elite Iran­ian gen­er­als. Iran’s Pres­i­dent Ebrahim Raisi said Wednes­day the at­tack “will not re­main with­out an­swer.”

Biden al­so re­newed his con­cerns about Ne­tanyahu’s plan to car­ry out an op­er­a­tion in the south­ern city of Rafah, where about 1.5 mil­lion dis­placed Pales­tini­ans are shel­ter­ing, as Is­rael looks to elim­i­nate Hamas fol­low­ing the mil­i­tant group’s dead­ly Oct. 7 at­tack. Vice Pres­i­dent Ka­mala Har­ris, Blinken and na­tion­al se­cu­ri­ty ad­vis­er Jake Sul­li­van al­so joined the call.

Still, the Biden ad­min­is­tra­tion has pro­ceed­ed apace with arms trans­fers and de­liv­er­ies to Is­rael, many of which were ap­proved years ago but had on­ly been par­tial­ly or not at all ful­filled. Just this week, on Mon­day, the De­mo­c­ra­t­ic ad­min­is­tra­tion’s “Dai­ly List” of mu­ni­tions trans­fers in­clud­ed the sale to Is­rael of more than 1,000 500-pound (225-kilo­grams) bombs and more than 1,000 1,000-pound (450-kilo­gram) bombs.

Of­fi­cials said those trans­fers had been ap­proved be­fore the pub­li­ca­tion of the list on Mon­day — the day Is­raeli airstrikes hit a World Cen­tral Kitchen aid con­voy in Gaza, killing sev­en of the group’s em­ploy­ees — and that they fell be­low the thresh­old for new con­gres­sion­al no­ti­fi­ca­tion. Al­so, they not­ed that the bombs are not for de­liv­ery to Is­rael un­til 2025.

Mean­while, the Pen­ta­gon on Thurs­day said plans to build a tem­po­rary pier off the coast of Gaza to help boost the flow of aid in­to the ter­ri­to­ry con­tin­ue to move for­ward. Maj. Gen. Pat Ry­der, Pen­ta­gon press sec­re­tary, said the pier will be on line by the end of the month or ear­ly May. Biden an­nounced plans to build the float­ing pier dur­ing his State of the Union ad­dress last month.

Ry­der said Is­rael has agreed to pro­vide se­cu­ri­ty on the shore as aid is trans­ferred and dis­trib­uted, but de­tails are still be­ing worked out.

Is­rael has ac­knowl­edged re­spon­si­bil­i­ty for the strikes but said the con­voy was not tar­get­ed and the work­ers’ deaths were not in­ten­tion­al. The coun­try con­tin­ues to in­ves­ti­gate the cir­cum­stances sur­round­ing the killings.

An­drés harsh­ly crit­i­cized the Is­raeli mil­i­tary for the strike, and his or­ga­ni­za­tion has paused its work in Gaza.

“The Is­raeli gov­ern­ment needs to stop this in­dis­crim­i­nate killing. It needs to stop re­strict­ing hu­man­i­tar­i­an aid, stop killing civil­ians and aid work­ers, and stop us­ing food as a weapon,” he wrote on X. “No more in­no­cent lives lost.”

The war in Gaza be­gan when Hamas-led mil­i­tants stormed in­to south­ern Is­rael, killing some 1,200 peo­ple, most­ly civil­ians, and tak­ing around 250 peo­ple hostage.

The Is­raeli mil­i­tary cam­paign in Gaza, ex­perts say, is among the dead­liest and most de­struc­tive in re­cent his­to­ry. With­in two months, re­searchers say, the of­fen­sive al­ready has wreaked more de­struc­tion than the raz­ing of Syr­ia’s Alep­po be­tween 2012 and 2016, Ukraine’s Mar­i­upol or, pro­por­tion­al­ly, the Al­lied bomb­ing of Ger­many in World War II. It has killed more civil­ians than the U.S.-led coali­tion did in its three-year cam­paign against the Is­lam­ic State group.