The United Nations Relief and Works Agency said Sunday that "thousands of people" have broken into several of their warehouses and distribution centers in the middle and southern parts of the Gaza Strip, "taking wheat flour and other basic survival items like hygiene supplies."

"This is a worrying sign that civil order is starting to break down after three weeks of war and a tight siege on Gaza," Thomas White, director of UNRWA affairs in Gaza, said in a statement. "People are scared, frustrated and desperate. Tensions and fear are made worse by the cuts in the phones and internet communication lines. They feel that they are on their own, cut off from their families inside Gaza and the rest of the world."

Since Oct. 7, a "massive displacement of people" who were forced to leave the north of Gaza and head southward due to Israeli airstrikes "has placed enormous pressure on those communities," according to UNRWA.

"Supplies on the market are running out while the humanitarian aid coming into the Gaza Strip on trucks from Egypt is insufficient," White added. "The needs of the communities are immense, if only for basic survival, while the aid we receive is meager and inconsistent."

As of Sunday morning, just over 80 trucks of humanitarian aid had crossed into Gaza from Egypt in one week. There was no aid delivered on Saturday due to a communications blackout in Gaza, according to UNRWA. The agency, which is the main actor for the reception and storage of aid in Gaza, said it was "not able to communicate with the different parties to coordinate the passage of the convoy."

UNRWA said its teams in Gaza have reported that internet services and connections were restored. The agency said it will reassess the situation with the goal of resuming aid convoys and distribution on Sunday.

"The current system of convoys is geared to fail," White said. "Very few trucks, slow processes, strict inspections, supplies that do not match the requirements of UNRWA and the other aid organizations, and mostly the ongoing ban on fuel, are all a recipe for a failed system. We call for a regular and steady flow line of humanitarian supplies into the Gaza Strip to respond to the needs especially as tensions and frustrations grow."

Meanwhile, UNRWA said 59 staff members have now been killed in Gaza since Oct. 7.

-ABC News' Guy Davies and Morgan Winsor

As internet service returned to Gaza on Sunday, several people inside the enclave spoke with ABC News, detailing an increase in aerial bombardments and tank shelling over the last two nights.

"When the internet went out, I felt very afraid and thought we would die and no one would know anything about us," said one resident, who asked not to be named for safety reasons.

Internet and telecommunications in Gaza, which had been disrupted Friday, were being "gradually" restored, Paltel Group, a local provider, said on social media early Sunday.

"For a moment, we thought it's the end," said another Gaza resident, who also asked that they not be identified.

The person added, "No way out. Complete darkness, no communication and the loud sound of missiles and bombardment."

-ABC News' Zoe Magee

Israeli Prime Minister Benjamin Netanyahu said the war in Gaza "will be long and difficult" as Israel expands its ground operations in the enclave.

"This is the second stage of the war, the goals of which are clear: Destroying Hamas's military and governing capabilities, and bringing the captives back home," Netanyahu said in a statement Saturday.

Netanyahu said the War Cabinet and Security Cabinet both decided to expand ground operations "based on a commitment to ensure both the destiny of the state and the security of our soldiers."

The prime minister said aerial strikes have intensified in recent days to "assist our forces in making a safer ground incursion."

"We have eliminated countless terrorists, including arch-terrorists, and we have destroyed many terrorist command posts and infrastructure. We are only just getting started," he said.

Israeli Prime Minister Benjamin Netanyahu met with the families of hostages held in Gaza for the first time on Saturday, on the heels of Israel's expanded ground operation.

Among those in attendance were the families of abducted children.

"My heart was broken. I reiterated to them: At every stage up to now and at every stage from now, we will exhaust every possibility to bring our brothers and sisters back to their families," Netanyahu said in a statement following the meeting.

According to Israeli military spokesperson Rear Adm. Daniel Hagari, 229 people captured in Israel are being held hostage in Gaza.