After a night of heavy airstrikes, the Israeli military announced Tuesday that its expanded operation in Gaza City "to destroy Hamas' military infrastructure" has begun, and warned residents to move south. Israeli military spokesman Avichay Adree announced the expansion of Israel's operation in a post on X, renewing a warning for Gaza City's famine-stricken residents to evacuate.

Many Palestinians -- tens of thousands of whom had sought shelter in Gaza City after fleeing areas further north amid Israel's offensive against Hamas -- have said they're unable to evacuate due to overcrowding in southern Gaza and the high price of transport.

The Israel Defense Forces announced the launch of the next stage of "Operation Gideon Chariots," saying two divisions had begun pushing into the heart of Gaza City, with two regular divisions operating in the surrounding area. It said a third division would join the operation in the coming days.

"They will surround Gaza City on all sides," the IDF said.

Hospital officials told The Associated Press that Israeli airstrikes overnight in northern Gaza killed at least 20 people.

Earlier in the day, Israeli Defense Minister Israel Katz said "Gaza is burning," as U.S. Secretary of State Marco Rubio left Israel for Qatar, where he planned to meet with officials still incensed over Israel's strike last week that killed five Hamas members and a local security official.

While Arab and Muslim nations denounced the strike at a summit Monday, they stopped short of any major action targeting Israel, highlighting the challenge of diplomatically pressuring any change in Israel's conduct in the grinding Israel-Hamas war.

Separately, a team of independent experts commissioned by the United Nations' Human Rights Council concluded that Israel is committing genocide in Gaza. It issued a report Tuesday that calls on the international community to end the genocide and take steps to punish those responsible for it.

Israel has refused to cooperate with the commission and has accused it and the HRC of anti-Israel bias. A statement from Israel's Foreign Ministry Tuesday says it "categorically rejects this distorted and false report."

Rubio, speaking to journalists before leaving Israel, also indicated that the ground offensive on Gaza City had begun.

"We think we have a very short window of time in which a deal can happen," Rubio said. "We don't have months anymore, and we probably have days and maybe a few weeks so it's a key moment -- an important moment."

"Our preference, our No. 1 choice, is that this ends through a negotiated settlement," he added, while acknowledging the dangers an intensified military campaign posed to Gaza.

"The only thing worse than a war is a protracted one that goes on forever and ever," Rubio said. "At some point, this has to end. At some point, Hamas has to be defanged, and we hope it can happen through a negotiation. But I think time, unfortunately, is running out."

Israel says Gaza City ground offensive against Hamas underway, as Rubio says time "running out" for peace deal