A senior U.S. military commander came to Israel on Thursday, authorities said, as fears ran high that Iran would soon conduct a strike to avenge the killings of three senior officers.

Iran’s authorities have frequently pledged to retaliate against Israel for an April 1 strike in Syria that killed several senior Iranian commanders. American officials have suggested they are bracing for a possible Iranian reaction, and Israel has put its military on alert.

The Israeli military launched what it called a precision operation to kill members of Hamas in Gaza on Thursday, a day after a strike that killed the family of one of the group’s most senior officials.

Ismail Haniyeh, who runs the political branch of Hamas from exile, said three of his sons had been killed in the Israeli attack in northern Gaza on Wednesday. Hamas-affiliated media said that three of Mr. Haniyeh’s grandkids were also murdered in the incident.

Samantha Power, the head of the U.S. Agency for International Development, told senators this week that a famine was starting in northern Gaza, which has been ravaged by six months of Israeli military operations and is the section of the territory most blocked off from help.

Ms. Power’s statement was noteworthy since it made her the first senior American official to officially designate the hunger situation in the Gaza Strip as a famine.

But her organization, known as U.S.A.I.D., eventually moved to soften Ms. Power’s comments, explaining that her evaluation was based on data obtained in March, not on new intelligence.

Six months into the Israel-Hamas war, the inhabitants of Gaza are confronting a hunger crisis that the United Nations warns borders on famine.

The situation in Gaza is totally man-made, a product of Israel’s war on Hamas and the near-complete closure of the region, humanitarian experts say.

Conflicts were also at the foundation of the other two disasters in the recent two decades that were defined by a global authority as famines in Sudan and Somalia, although in those countries, drought was also a significant underlying component.

UNICEF stated on Thursday that one of its cars had been “hit by live ammunition” this week as it was waiting to enter northern Gaza and that the agency had reported the problem with the Israeli authorities.

Tess Ingram, a spokeswoman for UNICEF, claimed she had been traveling with a convoy that came under fire on Tuesday while waiting to pass an Israeli gate going to northern Gaza.

No one in the convoy was hurt, Ms. Ingram said in an interview, but the firing underscored the ever-present risks for humanitarian workers in the enclave.

A senior Hamas official stated on Wednesday that Hamas did not have 40 living hostages in Gaza who matched the conditions for an exchange under a proposed cease-fire agreement with Israel being negotiated.

A senior Israeli official claimed Israel had relayed Hamas’s claim, and the senior Hamas official said that the group had informed mediators mediating the negotiations. The Israeli official and the Hamas official sought anonymity because of the sensitivity of the conversations.