The State Department was tracking the potential for a significant escalation in Israel’s military campaign in Gaza throughout the day but did not have confirmation that the Israel Defense Forces would expand its ground operations until around the time it was announced to the public earlier Friday, according to two U.S. officials.

Officials say the U.S. has been pressuring Israel to adopt a narrower scope for its offensive and take a more incremental approach. One source said that while Israeli forces seem likely to stay on the ground in Gaza for a longer duration this time, if this incursion doesn't spiral, it could be a positive sign that the administration is successfully making its case.

At this hour, there is still no clarity from the U.S. side on whether this is the big ground offensive that's been expected -- or just part of the buildup.

Officials are confident that they can keep up the short windows of calm that have allowed a limited amount of aid to flow into Gaza through the Rafah Gate, but these fall short of the sustained “humanitarian truce” the United Nations is demanding.

But several other delicate negotiations directly involving the U.S. -- including efforts to free the hostages, allow foreign nationals to exit Gaza and create safe spaces inside the enclave -- could be sidelined by a more comprehensive ground assault. Talks with all parties involved press on. Officials acknowledge that the U.S. would have liked to resolve these issues before any escalation, but that Hamas was likely to use its leverage to push off additional military action as long as possible.

-ABC News' Shannon K. Crawford

Doctors Without Borders made an urgent plea for protection of medical centers in Gaza, after the organization said it has lost contact with its members in the region.

In a video post on X, formerly known as Twitter, Avril Benoit, the organization's executive director, said she was very concerned about the patients, staff and civilians who are taking shelter at al-Shifa Hospital.

The Israel Defense Force said Hamas was using the hospital as a shield for its tunnels and ops centers.

"We call for the unequivocal protection of all medical facilities, staff and civilians across the Gaza Strip," she said. "We need an immediate cease-fire now."

UNICEF said it has also lost contact with its employees in Gaza and is "extremely concerned about their safety."

-ABC News' Cindy Smith

When asked whether troops had launched a ground invasion into the Gaza Strip on Friday night, Israel Defense Forces spokesperson Peter Lerner told ABC News, "We are conducting our sweep and clear activities in order to create better conditions for optimal operational conditions on the ground."

"So we are seeking out anti-tank capabilities, we are destroying observation posts and we are engaging the terrorists where we find them on the front lines or in the peripheral of the Gaza Strip," he continued, noting that troops have been "conducting these activities" for "several days" but he can't detail specifics due to "operational concerns."

"We intend on dismantling their capabilities, destroying their government, and making sure they can never use the Gaza Strip as a staging ground against our people again," Lerner added.

The United Nations General Assembly on Friday adopted a resolution calling for an "immediate, durable and sustained humanitarian truce" between Israel and Hamas.

The resolution also demands the "continuous, sufficient and unhindered" provision of supplies and services for civilians in Gaza, as Israel says it is expanding its ground operations in the territory.

Securing the release of the hostages being held in Gaza is still a priority as Israel expands its ground assault in the territory in an effort to defeat Hamas, the White House's national security adviser said Sunday.

"We are continuing to see if there are ways to make that happen. We are prepared to support humanitarian pauses so that hostages can get out safely. And we will keep working at that every day because the president has no higher priority than the safe return of American citizens and wants to support the return of citizens of other countries and Israelis, as well," Jake Sullivan told ABC "This Week" co-anchor Martha Raddatz.

"Now, how exactly that happens ... I cannot predict that. All I can tell you is every effort is being undertaken right now to do that," Sullivan said.

But he noted "there are ongoing efforts which I can't get into detail on television, including regional partners, including the Israelis."

-ABC News' Tal Axelrod