The Israel Defense Forces has announced that it has opened a new crossing to bring humanitarian aid into the famine-stricken Gaza.

The military announced in a Sunday press release the opening of the Western Erez crossing between Israel and northern Gaza in coordination with the U.S.

According to the military, the new crossing is located west of the Erez crossing, closer to the seashore. The crossing was constructed by the Israeli military "as part of the effort to increase routes for aid to Gaza, particularly to the North of the strip."

Earlier Sunday, IDF said it launched a large-scale operation in the area of Jabaliya in the North, while intensifying its military operations in the Eastern portion of Rafah and the Gaza side of the Rafah crossing. It said that it had called on the civilian population to evacuate from Jabaliya to shelters in the west part of Gaza City.

-ABC News' Dragana Jovanovic

In a phone call Sunday with his Israeli counterpart, White House National Security Advisor Jake Sullivan expressed an "ironclad U.S. commitment" to Israel but also voiced the Biden administration's concerns about Israel's major military operations in Gaza, according to the White House.

During the call with Israeli National Security Advisor Tzachi Hanegbi, Sullivan reiterated President Joe Biden's "longstanding concerns over the potential for a major military ground operation into Rafah, where over one million people have taken shelter," according to a readout of the call that was released by the White House.

"He [Sullivan] discussed alternative courses of action to ensure the defeat of Hamas everywhere in Gaza," the readout said. "Mr. Hanegbi confirmed that Israel is taking U.S. concerns into account."

The White House said Sullivan also expressed condolences on Israel's Memorial Day, the first since Hamas' surprise Oct. 7 attacks on Israel. The Hamas attack killed 1,200 people, most of them civilians, according to Israel's Prime Minister's Office.

Sullivan and Hanegbi also reviewed discussions by officials on both sides of the war about alternatives for a Rafah invasion and agreed to plan an in-person meeting soon, according to the White House.

-ABC News' Michelle Stoddart

More than 300,000 people have fled Rafah in the week since Israel issued a partial evacuation order, the United Nations agency operating in Gaza said on Sunday.

The U.N. Agency for Palestine Refugees called the evacuation "forced and inhumane."

"There is nowhere safe to go," the agency said on social media, repeating the phrase three times for emphasis.

The Israeli military late Saturday called again for civilians to evacuate from much of the eastern part of the city, which is in southern Gaza.

Israel Defense Forces entered Rafah last week, in what they called a "precise" operation ahead of potential invasion.

"Prior to our operations we urge civilians to temporarily move towards humanitarian areas and move away from the crossfire that Hamas puts them in," the Israel Defense Forces said on a post on Telegram. "Our war is against Hamas, not against the people of Gaza."

-ABC News' Dragana Jovanovic and Kevin Shalvey

An independent, self-formed task force of former State Department officials and international law experts say the U.S. "shirked" its legal obligations with Friday's National Security Memorandum-mandated report that examined Israel's use of U.S.-supplied arms.

"The Administration must come to terms with the fact that what it faces in its lethal military assistance to Israel's operations in Gaza - and beyond - is not a policy problem: it is a legal problem," the officials said Friday, adding, "The Administration’s report is at best incomplete, and at worst intentionally misleading in defense of acts and behaviors that likely violate international humanitarian law and may amount to war crimes. Once again, the Biden Administration has stared the facts in the face - and then pulled the curtains shut."

More than 34,000 Palestinians have died, including 14,000 children, the officials said, noting that "most of them [were] killed by U.S. munitions."

-ABC News' Christopher Boccia

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