The Biden administration gave Israel until mid-March to sign a letter, provided by the U.S. on Tuesday, that gives assurances it will abide by international law while using U.S. weapons and allow humanitarian aid into Gaza, three U.S. and Israeli officials told Axios.

Why it matters: The assurances are now a requirement under a memorandum issued earlier this month by President Biden. While it doesn't single out Israel, the new policy came after some Democratic senators expressed concern over the Israeli military campaign in Gaza. If the assurances aren't provided by the deadline, U.S. weapon transfers to the country will be paused.

Driving the news: The national security memorandum, published on Feb. 8, states that prior to supplying U.S. weapons, a country must give the U.S. "credible and reliable written assurances" that it will use any such weapons in accordance with international humanitarian law.

• It also stresses that a country that uses U.S. weapons in conflict areas needs to provide "credible and reliable written assurances" that it will "facilitate and not arbitrarily deny, restrict, or otherwise impede, directly or indirectly, the transport or delivery of United States humanitarian assistance and United States Government-supported international efforts to provide humanitarian assistance."
• Countries engaged in conflicts, like Israel, have 45 days from the day the memo was issued to provide the written assurances and have them certified by Secretary of State Tony Blinken. Other countries have 180 days.
• The memo requires the administration to provide an annual report to Congress on whether countries are adhering to international law.

Catch up quick: The memorandum was issued by the White House after pressure from Sen. Chris Van Hollen (D-Md.) and other senators who wanted to add these requirements as an amendment to the Senate supplemental funding bill.

• Three U.S. officials told Axios that Senate Majority Leader Chuck Schumer told the White House he was concerned that such an amendment would divide the Democratic caucus in the Senate and asked to take executive action instead.
• "Myself and the co-sponsors of the amendment made it clear to Majority Leader Schumer that we are determined to have a vote if we don't succeed in implementing it through executive action. That and the fact that it made sense on the merit of it, persuaded the administration that they should work with us on this," Van Hollen told Axios.

He said he held talks with White House national security adviser Jake Sullivan and other White House officials to draft the new memorandum, which was kept secret until it was published earlier this month.

• "We did it to make sure we have an accountability structure and that U.S. security assistance aligns with both our values and our interests," Van Hollen said.

Behind the scenes: U.S. officials in both Washington and Tel Aviv on Tuesday officially briefed their Israeli counterparts on the new policy and gave them the draft letter they need to sign to comply.

• A senior Israeli official said the U.S. request was to have the written assurances by mid-March so that Blinken can certify them by the end of the month. Israel can decide who in the government will sign the letter.
• Similar letters were given in recent days to several other countries that use U.S. weapons, a U.S. official said.

What they're saying: A State Department official said, "We continue to implement National Security Memorandum-20, including having discussions with our security cooperation partners around the world."

• A White House National Security Council spokesperson said "Israel has already indicated ... it anticipates being able to provide the relevant assurances."
• The spokesperson stressed that the assurances are not "Israel-specific" and the "timing is also expressly outlined" in the memorandum.
• The spokesperson added that the memorandum "did not impose new standards for military aid but instead provided a transparent, consistent structure for obtaining assurances for compliance with those preexisting standards."
• The Israeli Defense Ministry declined to comment.

Go deeper… Charted: U.S. has provided Israel with more than 70,000 weapons since 1950

Editor's note: This story has been updated with additional details from the NSC.