The blockade of supplies into Gaza continues, according to a spokeswoman for the United Nations Relief and Works Agency.

"No fuel, no food, no water, and no other kind of aid," Juliette Touma, the spokeswoman for the UNRWA, said in a statement.

The UNRWA also estimated the number of displaced people in Gaza at 1 million people and denied reports of fuel entering through Rafah.

Senate Majority Leader Chuck Schumer, fresh off his return from Israel, harshly condemned the Hamas attacks on Israel and repeatedly insisted that the Senate act quickly to provide an aid package to Israel.

In the coming days, Schumer said he'd work with the administration to craft a package that includes military, humanitarian, intelligence and diplomatic aid. The administration has not yet presented a formal ask for Israeli relief, but Schumer said in a conversation with Israeli leaders, he's learned what the nation needs most.

He also said it's incumbent on the Senate to begin work on the package to "give Israel the tools it needs to defend itself" and to move on it quickly, even as the House remains without a speaker. He said supporting Israel must be "at the front and center of our attention."

-ABC News' Allison Pecorin

Ronen Bar, director of Israel's Shin Bet security service, said in a letter, "We were unable to generate a sufficient warning" for Hamas' attack.

"As the one who is at the head of the organization -- the responsibility for this is mine," he wrote.

Bar said there will be time for an investigation, but for now, Israelis are fighting.

-ABC News' Will Gretsky

A large group of protesters are rallying outside the White House calling for a cease-fire in Gaza.

More than 30 people have been arrested, according to the U.S. Secret Service.

The organizers of the rally said protesters came from all over the country to "protest for peace." Two demonstrators said they felt President Joe Biden's handling of the crisis has been "shameful" and "catastrophic."

The president has emphasized that Hamas does not represent all Palestinian people, who are also suffering, but some protesters told ABC News they didn't think Biden's language was strong enough.

-ABC News' Selina Wang

Hamas fighters are believed to be "still hiding" in some communities in southern Israel even after the Israeli military took back control, according to Israel Defense Forces spokesman Maj. Doron Spielman.

"We are in control of the communities, but we actually assume that there are Hamas terrorists that are still hiding in these areas, including in the road where we are now," Spielman told ABC News during an interview Monday in Sderot, Israel. "In all these communities, we've seen terrorist come out of hiding. Just yesterday, they took over an ambulance."

"We're still being very, very careful," he added. "This is a war zone with active terrorists that are operating here."

Sderot is a southwestern Israeli city located near the county's border with the Hamas-ruled Gaza Strip. A police station there was stormed by Hamas fighters on Saturday as part of the militant group's wider incursion, leaving at least six Israeli police officers dead. The IDF then bombed the police station with the Hamas fighters inside, demolishing it.

Hamas fighters and other Palestinian militants are "striking strategic locations" along the border fence, allowing them to drive through in pickup trucks, Spielman said. Civilians in some of the local communities have been ordered to evacuate, while others have left voluntarily, according to Spielman.

"We do have a lot of ground troops in this area. We have a lot of tanks. We have, in addition, artillery. And we're prepared forever for anything," he said. "And if it happens, the next stage, it's going to happen here because this is the area that was the flashpoint and this is the area we're going to be presenting ourselves and finishing this battle. We, of course, have no choice but to finish."

When asked about the mounting casualties of Palestinian civilians in Gaza as a result of the IDF's retaliatory airstrikes, Spielman said: "We always try to avoid civilian casualties. However, I would say that this is war and our first priority here is to destroy Hamas."

-ABC News' Angus Hines and Ian Pannell