Israeli Minister of Defense Yoav Gallant signed on Thursday a letter to the Biden administration assuring Israel will use U.S. weapons according to international law and allow U.S.-supported humanitarian aid into Gaza, two Israeli and U.S. officials told Axios.

Why it matters: The letter of assurances is a requirement under a national security memorandum issued last month by President Biden. The new policy doesn't single out Israel, but it came after some Democratic senators expressed concern over the Israeli military campaign in Gaza.

Driving the news: The Biden administration asked Israel to provide the signed letter of assurances by mid-March. Secretary of State Antony Blinken now has until March 25 to certify that Israel's written commitments are credible. If certification isn't given, U.S. weapons transfers to Israel will be suspended.

• The Israeli war cabinet gave Gallant the green light to sign the letter of assurances last Sunday.
• But the defense minister only signed it on Thursday. It was then delivered to the U.S. ambassador to Israel, Jack Lew, an Israeli official said.
• The Israeli Ministry of Defense declined to comment.

Catch up quick: 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."

Behind the scenes: Israeli and U.S. officials told Axios Israel asked the Biden administration to add to the written assurances another letter from the Biden administration that stresses U.S. commitment to Israel's security, for Israel's right to defend itself and for U.S. military assistance to Israel.

• Biden administration officials told the Israelis that such a request will require a long process of consultations and negotiations that will not meet the deadline set in the memorandum.
• U.S. officials also said they told the Israelis that they'd rather keep this process as technical as possible and not turn it into more political negotiations that might require Israel to give more written assurances of its own.

What to watch: Last week a group of House Democrats made the case to Biden that an Israeli invasion of Rafah could violate his requirement that U.S. military aid be used in accordance with international law.

• In a letter to Biden, more than three dozen House Democrats argued an invasion of Rafah "would likely contravene" the national security memorandum, noting the "the absence of a credible plan" to protect civilians.