JERUSALEM — Secretary Blinken vowed American support to Israel on Thursday during a visit to the Jewish state as its military hit the Hamas-ruled Gaza Strip with airstrikes and prepared for a possible ground invasion. 

“You may be strong enough on your own to defend yourselves, but as long as America exists you will never have to,” Mr. Blinken said after meeting with Prime Minister Netanyahu at Tel Aviv. “We will always be there by your side.”

Echoing earlier remarks made by Mr. Netanyahu, Mr. Blinken called it “a moment for moral clarity,” adding that any “failure to unambiguously condemn terrorism puts at risk not only people in Israel, but people everywhere.”

The state secretary pointed to the international scope of the weekend terrorist attack, including “individuals from 36 countries killed or missing,” from “Europe, Asia, Africa, the Americas – no region has escaped Hamas’s bloody reach.”

He added that “anyone who wants peace and justice must condemn Hamas’s reign of terror.”

Mr. Blinken framed his remarks in a personal context, noting that he was speaking “not only as the United States Secretary of State, but also as a Jew.” He explained that his “grandfather, Maurice Blinken, fled pogroms in Russia.” Mr. Blinken’s stepfather, he said, “survived concentration camps – Auschwitz, Dachau, Majdanek.”

This family history means, Mr. Blinken continued, that “I understand on a personal level the harrowing echoes that Hamas’s massacres carry for Israeli Jews – indeed, for Jews everywhere.”

Mr. Blinken’s visit underscores American backing for Israel’s retaliation against the terrorist organization.

Mr. Blinken is to meet Friday with Palestinian leader Mahmoud Abbas, whose authority is confined to parts of the West Bank, and King Abdullah II of Jordan.

Mr. Netanyahu has vowed to “crush” Hamas after terrorist attackers stormed into the country’s south on Saturday and massacred hundreds of people, including killings of children in their homes and young people at a music festival. Mr. Netanyahu marked Hamas atrocities, including beheading soldiers and raping women.

Amid grief and demands for security among the Israeli public, the government is under intense pressure to topple Hamas rather than continuing to try to bottle it up in Gaza.

Four previous conflicts ended with the group still firmly in control of Gaza, which it has ruled since 2007. Israel has mobilized 360,000 reservists, massed additional forces near Gaza, and evacuated tens of thousands of residents from nearby communities. 

A new war Cabinet, which includes a longtime opposition politician, is now directing the fight.

As Palestinians in Gaza tried to stock up on bread and groceries amid dwindling supplies, Israel said nothing would be allowed into the district until the approximately 150 hostages taken captive by Hamas during a weekend attack are freed.

International aid groups warned of a worsening humanitarian crisis.

“Not a single electricity switch will be flipped on, not a single faucet will be turned on, and not a single fuel truck will enter until the Israeli hostages are returned home,” Israel’s energy minister, Israel Katz said on social media.

An Israeli military spokesman, Lieutenant Colonel Richard Hecht, told reporters Thursday that forces “are preparing for a ground maneuver” should political leaders order one. 

A ground offensive in Gaza, where the population is densely packed into a sliver of land only 25 miles long, could lead to casualties on both sides in anticipated house-to-house fighting.

As Israel strikes Gaza from the air, Hamas has been firing thousands of rockets into Israel. Amid concerns that the fighting could spread in the region, Syrian state media reported that Israeli airstrikes on Thursday hit international airports in the Syrian capital, Damascus, and in the northern city of Aleppo, putting them out of service.

The Israeli military said overnight strikes targeted Hamas’ elite Nukhba forces, including command centers used by the terrorists who attacked Israel on Saturday, and the home of a senior Hamas naval operative that it said was used to store unspecified weapons. 

Other airstrikes killed commanders from two smaller militant groups, according to press linked to those organizations.

“Right now we are focused on taking out their senior leadership,” Lieutenant Colonel Hecht said of Hamas. “Not only the military leadership, but also the governmental leadership, all the way up to (top Hamas leader Yehya) Sinwar.”

The Israeli military says more than 1,300 people, including 222 soldiers, have been killed in Israel, a staggering toll unseen since the 1973 war with Egypt and Syria that lasted weeks. 

More than 1,400 Palestinians have been killed in Gaza, the Hamas-controlled Gaza health ministry said. The Israeli military reports that hundreds of those killed were Hamas members. An additional 1,500 Hamas terrorists were killed inside Israel.