KHAN YOUNIS, Gaza Strip — The Israeli military raided Gaza’s largest hospital early Wednesday, conducting what it called a “precise and targeted operation against Hamas in a specified area” of the facility, which has been the site of a standoff.

Israeli authorities claim that Hamas conceals military operations in the Shifa Hospital. Yet with hundreds of patients and medical personnel inside, the military had until now refrained from entering.

The White House’s national security council spokesman, John Kirby, said America has unspecified intelligence that Hamas and other groups use Shifa and other hospitals and tunnels underneath them to support their terrorist attacks and hold hostages.

The intelligence is based on multiple sources, and the U.S. independently collected the information, an American official said on the condition of anonymity to discuss sensitive matters.

In recent weeks, Israeli defense forces have publicly warned that such use of the hospital “jeopardizes its protected status under international law,” the military said. On Tuesday, military officials conveyed again to Gaza authorities that all military activity in the hospital must cease within 12 hours. “Unfortunately, it did not,” the military said.

Hamas has denied the Israeli accusations that it uses the hospital for cover. Israeli military officials gave no further details but said they were taking steps to avoid harm to civilians.

The operation unfolded after the Israeli military seized broader control of northern Gaza on Tuesday, including capturing the territory’s legislature building and its police headquarters, in gains that carried high symbolic value in the Jewish state’s quest to crush Hamas.

Inside some of the captured buildings in Gaza, soldiers held up the Israeli flag and military flags in celebration. In a nationally televised news conference, the Defense minister, Yoav Gallant said Hamas had “lost control” of northern Gaza and that Israel had made significant gains in Gaza City.

Asked about the time frame for the war, Mr. Gallant said: “We’re talking about long months, not a day or two.”