Secretary of State Antony Blinken and Secretary of Defense Lloyd Austin wrote a letter to two Israeli officials over the weekend, informing them that Israel had to improve the humanitarian situation in Gaza, particularly in the northern part of the enclave, or risk violating U.S. law regarding U.S. foreign military sales.

The secretaries wrote that they gave Israel 30 days to “reverse the downward humanitarian trajectory and consistency with its assurances to us” and warned that “failure to demonstrate a sustained commitment to implementing and gaining these measures may have implications for U.S. policy” under relevant law.

John Kirby, National Security Council coordinator, said Tuesday that the letter was “not meant as a threat” but “meant to reiterate the sense of urgency we feel about the seriousness with which we feel it about the need for an increase, dramatic increase, in humanitarian assistance.”

The letter was prompted by a “relatively recent decrease in humanitarian assistance reaching the people of Gaza, which is obviously something we’ve been very, very concerned about conflict,” he added.

“We have not seen sufficient results over the past few weeks,” noting that the amount of aid getting into Gaza “has fallen by over 50% from where it was at its peak,” State Department spokesman Matthew Miller said Tuesday.

U.S. officials have expressed concerns about getting humanitarian aid to Palestinians affected by the war repeatedly over the course of Israel’s war in Gaza against Hamas. An overwhelming majority of the population have been displaced, many several times, while they also face limited food, clean water, and medicine.

Gaza is bordered by the Mediterranean Sea, Israel, and Egypt, though Israel currently controls the Egyptian-Gaza border from the Gaza side. Israel has limited the amount of aid that has gotten through various checkpoints between Israel and Gaza.

The Biden administration urged Israel to allow more aid in April, and U.S. officials have said the Israelis heeded those requests at the time.

Israel has repeatedly ordered Palestinians to evacuate from northern Gaza, though hundreds of thousands of people remain. Israeli officials considered a plan to effectively cut off northern Gaza and starve the remaining Hamas fighters of needed resources. However, the plan would likely include cutting civilians off from the aid they needed, too. Israeli Defense Minister Yoav Gallant told Austin over the weekend that Israel wouldn’t be implementing that plan, according to Axios.

The United States also had conversations with its Israeli counterparts to do more to ensure the safety of those who distribute the aid, especially after an errant Israeli strike hit a convoy of marked vehicles, killing several aid workers. Hundreds of aid workers have been killed throughout the war.

In an effort to get more aid into the strip, Biden directed the military to build a pier in the Mediterranean Sea to create a formal maritime aid option that did not rely entirely on the Israelis. The pier allowed for the transportation of enough food to feed about 450,000 people for one month, much less than its goal, after bad weather repeatedly shut down its operations and limited its availability.