The Pentagon said it still hasn’t seen a "credible" plan from Israel on how it will protect some 1 million civilians in Rafah in the case of an invasion.

"We've seen kind of a concept, but nothing detailed at this point," Pentagon press secretary Maj. Gen. Pat Ryder told reporters Monday morning.

He noted that the subject was raised Sunday by Defense Secretary Lloyd Austin in a phone call with Israel's defense minister, Yoav Gallant, but he declined to say what policy changes the U.S. might consider if Israel begins a full-scale invasion of Rafah without that credible plan.

Austin is scheduled to testify Wednesday, the same day the administration is required by law to tell Congress whether it agrees with Israel that its government complies with humanitarian law.

"I think there are still concerns in terms of the, again, given the number of people there and how you're going to take into account the safety and well-being of the million-plus people that are in Rafah as any operation commences," Ryder said. "Again, we agree with our Israeli partners on the importance of defeating Hamas and preventing them from being able to conduct attacks like they've done in the past. But we want to see that operation done in a way that again, takes into account civilians, takes into account how you're going to evacuate them off the battlefield. So those conversations will continue."

-ABC News' Anne Flaherty

President Joe Biden spoke with Israeli Prime Minister Benjamin Netanyahu on Monday, a source confirmed to ABC News.

Biden was expected to again reiterate his position on Rafah, urging restraint when it comes to an invasion of the enclave holding more than 1 million Gaza refugees, as he did when they last spoke on April 28.

Click here to read more about the conversation.

-ABC News' Mary Bruce and Justin Gomez

Israeli military jets targeted areas of Rafah overnight, striking "terror targets" and military structures, including a sniper's nest, the Israel Defense Forces said Monday.

The strike included areas of Rafah "from which projectiles were launched toward the area of Kerem Shalom yesterday," IDF officials said on Telegram.

There were no immediate reports of injuries following Monday's strikes. IDF strikes on Sunday had killed at least 12 people in Rafah.

-ABC News' Kevin Shalvey and Joe Simonetti

Israeli aircraft on Monday began dropping flyers in eastern Rafah, warning thousands of people sheltering in the city that they may be in danger ahead of a possible Israeli operation.

"The IDF will be operating against the terrorist organizations in the area where you are located, as it has operated until now," the flyers read in Arabic, according to a translation provided by the Israel Defense Forces. "Anyone found near terrorist organisations endangers themselves and their family members."

The flyers included directions for an evacuation, including information about the humanitarian area near Al-Mawasi, Israel said.

-ABC News' Joe Simonetti and Kevin Shalvey

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