Israel-Hamas War Live Updates: Israel Says It Has Isolated Gaza City

Israel has described Gaza City, in the north of the enclave, as a center for Hamas’s military operations, and its encirclement of the city appeared aimed at cutting it off from the rest of the strip. “Essentially today there is a northern Gaza and a southern Gaza,” Admiral Hagari said.

Journalists’ reports were limited by the blackout, but the BBC said one of its Gaza reporters thought the night had brought “the most intense airstrikes since the beginning of the war,” which it said were largely focused in northwest Gaza. And Wafa, the official Palestinian news agency, reported “violent explosions and an unprecedented bombardment by Israeli aircraft and warships,” saying the raids targeted the vicinities of several hospitals and had killed and injured dozens of people.

On Monday morning, NetBlocks, a monitoring service, said that “internet connectivity is being restored” in Gaza, about 15 hours after the blackout began, although service was still significantly disrupted. The group said it was the second longest such cutoff in the month since the war began.

Admiral Hagari said that the operation on Sunday night was searching for senior Hamas commanders. Earlier in the day, the Israeli military had accused Hamas of using two hospitals in northern Gaza, the Sheikh Hamad and Indonesian hospitals, as cover for its operational centers. The claim could not immediately be verified.

The Israeli military had earlier made similar accusations about Al Shifa Hospital, in Gaza City, and on Friday the Israeli military confirmed an airstrike near that facility. Hamas rejected the assertions about Al Shifa at the time, saying Israel had provided no evidence.

The Palestine Red Crescent Society, an independent aid group, said on social media that the blackout affected more than two million civilians, cutting off access to emergency medical services, and that, as during the previous blackouts, it had lost contact with its teams in Gaza.

The director general of the World Health Organization, Tedros Adhanom Ghebreyesus, said it was “very concerned” about the communications outage and the reports of heavy bombardment.

“Without connectivity, people who need immediate medical attention cannot contact hospitals and ambulances,” Dr. Tedros said on social media. “All channels of communication must be restored immediately.”

The director of NetBlocks, Alp Toker, said in an interview on Sunday that his organization was unable to immediately determine whether the blackout had been caused by Israel taking technical measures against Gaza’s telecommunications infrastructure or by physically damaging it. However, he noted that in the previous blackouts, the restoration of service had come “almost instantaneously,” suggesting physical repairs were not necessary. Paltel, the Gazan telecommunications provider, said it had made no repairs to restore connectivity after the first blackout.

The loss of connectivity in Gaza on Sunday was “technically fully consistent” with the previous two blackouts, Mr. Toker said.

The first blackout on Oct. 27, which began around sunset, lasted nearly 36 hours and spread fear and panic across Gaza as Israel began a ground invasion. After connectivity was restored, two American officials, speaking on the condition of anonymity because of the sensitivity of the issue, said the United States believed that Israel had been responsible for the cutoff and had urged Israeli counterparts at the time to restore service.