The U.N. Agency for Palestine Refugees said Monday it wouldn't begin to evacuate its staff from Rafah, adding that a possible Israeli invasion into the refugee city would be "devastating."

"UNRWA is not evacuating: the Agency will maintain a presence in Rafah as long as possible & will continue providing lifesaving aid to people," the group said in a statement.

An invasion into the city "would mean more civilian suffering & deaths," the agency said.

-ABC News' Kevin Shalvey

Israeli military officials on Monday issued a warning to civilians in eastern Rafah to begin a "gradual movement" to a humanitarian area.

"Calls to temporarily move to the humanitarian area will be conveyed through flyers, SMS messages, phone calls and media broadcasts in Arabic," Israel Defense Forces officials said in a statement posted to social media.

Israel said a humanitarian area around Al-Mawasi, a coastal town, had been expanded "to accommodate the increased levels of aid flowing into Gaza." That aid included new field hospitals and additional food and water, IDF officials said.

Prime Minister Benjamin Netanyahu had said last week that Israel would call for an evacuation of civilians prior to beginning its planned invasion into the southern Gaza city. Israeli officials haven't yet detailed a timeline for the expected operation.

"The IDF will continue pursuing Hamas everywhere in Gaza until all the hostages that they're holding in captivity are back home," IDF officials said Monday.

-ABC News' Kevin Shalvey

Hamas said Sunday that negotiations in Cairo have concluded and that its delegation will leave Cairo tonight.

A new report from the United States Departments of State and Defense said that given "Israel's significant reliance on U.S.-made defense articles" it is "reasonable to assess" that some have been used in instances "inconsistent" with Israel's obligation under international law.

The assessment, which came as part of a report ordered by President Joe Biden, examined the use of U.S.-supplied arms in active conflict zones, and also said that the U.S. could not compile enough evidence to prove that the country used American defense articles in violation of international humanitarian law.

"We do not have complete information to verify whether US defense articles covered under NSM-20 were specifically used in actions that have been alleged as violations of IHL (international humanitarian law) or international human rights law during the period of the report," the document says. "The nature of the conflict in Gaza makes it difficult to address or reach conclusive findings on individual incidents."

While the report said the Israeli government has "the knowledge, experience, and tools" to implement "best practices for mitigating civilian harm," the high number of civilian casualties "raise substantial questions about whether the IDF is using them effectively in all cases."

Additionally, the report noted that Israel did not cooperate with U.S. efforts to ramp up humanitarian aid and distribution in Gaza during the initial months of the conflict, but that officials have observed improvements.

-ABC News' Shannon Crawford and Anne Flaherty