BEIRUT -- Israel began a ground offensive into Gaza City, military officials said Tuesday, slow-rolling into the beleaguered city from multiple directions despite international opprobrium and even as hundreds of thousands of Palestinian residents remain within Gaza's devastated confines.

Weeks of intense bombardment that all but leveled the Gaza Strip's largest urban center made way for what Israeli military officials said was the ground maneuver phase of the operation to occupy the city.

"We are determined and offensive. We have defeated Hamas militarily wherever we have fought them, and we will act until Hamas rule is dismantled," the Israeli military statement said.

Two divisions -- comprising tens of thousands of soldiers -- began entering the city late Monday from its western flank, with two other divisions encircling the city. Some 130,000 reservists are expected to be mobilized in the coming days, the Israeli military said.

"Gaza is burning," Israeli Defense Minister Israel Katz said in a post on X. "We will not relent or turn back until the mission is complete."

Residents reported the Israeli military dispatched what they called "booby-trapped robots" -- armored personnel carriers filled with explosives repurposed as unmanned drones -- into city neighborhoods. Military officials quoted in Israeli media say troops are proceeding with caution, with the expectation of some 2,000 Hamas fighters bunkered in the city.

The operation went ahead despite widespread condemnation from Israel's European allies and accusations internationally that it was committing genocide, according to a U.N. commission report released on Tuesday. Israel rejected the commission's findings.

Germany, one of Israel's staunchest supporters, excoriated the decision to occupy Gaza City.

It is "the completely wrong path," German Foreign Minister Johann Wadephul said in a news briefing on Tuesday.

"We reject this and have made this clear to the Israeli government," Wadephul said. He urged the Israeli government to "return to the path of negotiations for a ceasefire and an agreement."

Wadephul appealed to the Israeli government to instead return "to the path of negotiations for a ceasefire and an agreement" on the release of captives held in Gaza.

In Israel, the decision to launch the offensive -- taken by the cabinet of Israeli Prime Minister Benjamin Netanyahu in August -- continues to be a contentious matter that has divided the military leadership and spurred demonstrations against Netanyahu. On Tuesday morning, families of hostages kidnapped by Hamas protested in front of Netanyahu's house in Jerusalem.

Despite the pummeling and repeated warnings that the roughly 1 million Gaza City residents should flee south to so-called humanitarian areas, more than two-thirds remain, according to Israeli military estimates.

"Escape is impossible for many. ... People left behind have been handed a death sentence," said Christoph Lockyear, secretary-general of Doctors Without Borders, known as MSF, in a statement on Monday. He added even those who survived the bombardment on their journey to southern Gaza would "find neither safety nor the basics they need to exist."

"What is happening in Gaza is not just a humanitarian catastrophe, it is the systematic destruction of a people. MSF is clear: Israel is committing genocide against Palestinians in Gaza, and doing so with absolute impunity."

Many residents also say they cannot afford to go to al-Mawasi encampment, the area south of the enclave designated by the Israeli military as a safe zone. Even if they did, overcrowding means there's no shelter to be found or even a space for tents; and Israeli strikes have hit safe zones in the past.

Nevertheless, news broadcasts on location on the coastal highway south of Gaza City showed a deluge of thousands of vehicles, many straining under haphazardly piled towers of mattresses, plastic chairs, bags of clothing -- anything people could save from their homes ahead of what is expected to be the city's complete destruction.

Health authorities in the enclave said 82 people were killed and wounded in the first hours of the offensive, and that emergency rooms in Gaza City's few remaining hospitals were extremely crowded and suffering shortages in medications and blood units.

As Israeli armor advanced into Gaza, U.S. Secretary of State Marco Rubio was traveling from Tel Aviv to Doha on Tuesday morning, where he hopes to assuage Qatar's ire over an Israeli strike on the Qatari capital targeting Hamas leaders last week.

In response to the strike, Qatar had threatened to suspend its longtime mediation efforts between Hamas and Israel. During a summit of Arabic and Islamic States on Monday held in Doha, its leaders berated Israel and demanded concrete punitive actions. (A collective communique from the summit announced little more than condemnation.)

But Rubio said he hoped would continue shepherding negotiations.

"If any country in the world can help mediate it, Qatar is the one," he said.

He added Hamas had a "very short window of time in which a deal can happen," and that the Trump administration's preference was for a negotiated settlement.

Hamas dismissed his words in a statement on Tuesday, saying Netanyahu bears "full responsibility" for the hostages' lives, and that the U.S. used a "policy of deception" to cover up Israeli "war crimes."

Israel demands the group hand back all hostages, surrender and disarm. Hamas insists on a ceasefire with negotiations that would lead to an exchange of hostages and Palestinian detainees in Israeli prisons and Israeli troops' withdrawing from the Gaza Strip; disarmament would happen when Israel agrees to the creation of an independent Palestinian state.

The war sparked on Oct. 7, 2023, when Hamas militants attacked southern Israel, killing some 1,200 people -- two thirds of them civilians, Israeli tallies say -- and kidnapping 251 others.

Israel retaliated with a full-on offensive that pulverized wide swaths of the enclave and has so far killed more than 62,000 people, the grand majority of them civilians, according to Gaza health authorities and aid groups; the Israeli military's former chief of staff said in a recent interview more than 200,000 people have been killed or injured -- more than 10% of Gaza's 2.2 million population, a figure that aligns with the Palestinian Health Ministry's estimates.

Israel says it has begun ground offensive in Gaza City, moving in thousands of troops