President Biden told Israeli Prime Minister Benjamin Netanyahu when they spoke on Thursday that "an immediate ceasefire" is needed to "protect innocent civilians" in Gaza and improve the humanitarian situation, the White House said.

Why it matters: Biden is making his strongest push for an end to the fighting in Gaza in six months of war, and warning for the first time that U.S. policy on the war will depend on Israel's adherence to his demands.

Driving the news: The call came three days after an Israeli strike killed seven World Central Kitchen aid workers, and with Biden under growing pressure from members of his own party to push for a ceasefire and ensure Israel does more to allow aid into Gaza.

• Biden "emphasized that the strikes on humanitarian workers and the overall humanitarian situation are unacceptable," per the readout.
• Biden also told Netanyahu that Israel must "announce and implement" a series of "concrete and measurable steps" to protect aid workers and address humanitarian suffering.

The key line: "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."

• Secretary of State Tony Blinken echoed that point in a press conference of his own on Thursday, saying: "If we don't see the changes we need to see, there will be a change in our policy."

Zoom in: After the call, White House spokesperson John Kirby said the steps the U.S. expects Israel to take include increasing the amount of aid that gets into Gaza, opening additional crossings to Gaza, "movement toward a ceasefire," and better protecting civilians and aid workers.

• "If there are no changes in their policy there will have to be changes in ours," Kirby said.

Behind the scenes: A source familiar with the call said it was "tense and challenging" and lasted more than 30 minutes.

• Kirby called it "direct, businesslike and professional."

Between the lines: Biden had previously been careful to make clear that his calls for a ceasefire were conditioned on a deal to bring Israeli hostages home.

• In Thursday's readout, the White House didn't fully link those issues but stressed the president "urged the Prime Minister to empower his negotiators to conclude a deal without delay to bring the hostages home."

What to watch: Sen. Chris Coons (D-Del.), one of the top Democratic backers of Israel and close ally to President Biden, said for the first time on Thursday that he was open to conditioning aid based on how Israel conducts the war.