The United States dispatched its top military commander for the Middle East to Israel on Thursday, after President Biden stated that, despite recent friction, American support for Israel “is ironclad” in the event of an attack by Iran.

Iran’s leaders have repeatedly vowed to punish Israel for an April 1 strike in Syria that killed several senior Iranian commanders. Israel has put its military on alert, and Mr. Biden said on Wednesday that Iran was threatening a “significant” attack.

Gen. Michael E. Kurilla, the American commander, will coordinate with Israel on what is widely expected to be imminent retaliatory action by Iran and will also discuss the war against Hamas in Gaza and humanitarian aid operations there, according to officials who spoke on the condition of anonymity because of the sensitivity of the matter.

Prime Minister Benjamin Netanyahu of Israel acknowledged on Thursday that Israel was facing “challenging times,” noting that “in the midst of the war in Gaza” his country was “also prepared for scenarios involving challenges in other sectors.”

“We have determined a simple rule: Whoever harms us, we will harm them,” he said while visiting an air base, using language that has been used in recent days to refer to threats from Iran and its proxies, including Hamas.

Active fighting in Gaza has ebbed to its lowest point since November. Israel withdrew troops from southern Gaza over the weekend but said the military would stay in other parts of the territory to preserve its “freedom of action and its ability to conduct precise intelligence-based operations.”

Mr. Netanyahu has said that a date has been set for a ground invasion of Rafah in southern Gaza, where more than a million displaced Palestinians have sought shelter — an operation U.S. officials have warned would be catastrophic for civilians. Some analysts have suggested that his threats are bluster or attempts at gaining leverage in cease-fire negotiations.

The Biden administration has urged Mr. Netanyahu to shelve the invasion plans and focus on “alternative approaches that would target the key elements of Hamas.”

President Biden has become increasingly critical of Mr. Netanyahu’s conduct of the war in Gaza, even threatening to condition U.S. assistance on Israel’s doing more to protect civilians. But he emphasized on Wednesday that American support for Israel in the face of danger from Iran and its allied militias, like Hezbollah, was unconditional.

“As I told Prime Minister Netanyahu, our commitment to Israel’s security against these threats from Iran and its proxies is ironclad,” he said at a news conference.

Secretary of State Antony J. Blinken also “made clear that the U.S. will stand with Israel against any threats by Iran and its proxies” when he spoke by phone on Wednesday with Israel’s defense minister, the State Department said.

In Israel, General Kurilla had carried out a situational assessment and reviewed “regional security challenges” with the Israeli military’s chief of staff, said Rear Adm. Daniel Hagari, the chief spokesman for the Israeli military.

“We are highly alert and ready to face various scenarios,” Admiral Hagari said in a televised news briefing, adding that any strike from Iranian territory would be a clear regional escalation.

As Iran and Israel have traded fresh threats in recent days, diplomats have been trying to reduce tensions and avert a wider regional war.

The foreign minister of Germany, Annalena Baerbock, spoke to her Iranian counterpart “about the tense situation” in the Middle East on Thursday, according to her office.

“Avoiding further regional escalation must be in everyone’s interest,” her office said in a statement. “We urge all actors in the region to act responsibly and exercise maximum restraint.”

The diplomatic efforts came as the Israeli military on Thursday announced that it had carried out a new operation that killed at least one member of Hamas in Gaza.

The Israeli military said Thursday that its forces had carried out a “precise, intelligence-based operation” in central Gaza overnight with fighter jets and ground troops to “eliminate terrorist operatives and strike terrorist infrastructure.”

“The goal of the operation, of course, is to destroy Hamas’s ability to rehabilitate itself in the area,” Admiral Hagari said. “We continue fighting in Gaza and are preparing for future operations.”

On Wednesday, an Israeli airstrike in northern Gaza killed three sons of Ismail Haniyeh, who leads the political wing of Hamas from exile. Hamas-affiliated media reported that three of Mr. Haniyeh’s grandchildren also were killed in the attack.

The Israeli military said the three sons — Amir, Mohammad and Hazem — were active in Hamas’s military operations, Amir as a cell commander and his brothers as lower-level operatives. One of the brothers was also involved in holding hostages in Gaza, the Israeli military said, without specifying which one. The military did not provide further details, and its claims could not be verified.

The military’s emphasis on the precision of the attack announced on Thursday followed accusations that Israeli bombing has been indiscriminate, causing avoidable civilian casualties, and amid rising criticism over impending famine in Gaza.

It also came as international negotiators worked to broker a cease-fire in Gaza and to secure the release of the hostages held in the enclave, in return for the release of Palestinians held in Israeli prisons. Those talks have stalled over disagreements about the details, with a senior Hamas official saying Wednesday that the group did not have 40 living hostages who met the criteria for an exchange under a proposal being discussed.

While Mr. Haniyeh is one of Hamas’s most senior officials, analysts said that his sons were not likely as integral to the group’s operations as the Israeli military has suggested.

“His son’s names are not usually floated around when you talk about seniority in Hamas, whether it’s the political or military wing,” said Tahani Mustafa, a senior analyst at the International Crisis Group, a think tank.

Bilal Saab, an associate fellow in the Middle East and North Africa program at Chatham House, said the strike on the sons might have been intended to placate a domestic audience in Israel or to give the Israelis leverage in the talks.

“It’s a political win for Israel more than anything else,” Mr. Saab said of the killings.

Mr. Haniyeh said Wednesday that Israel was “delusional if it thinks that by killing my children, we will change our positions” in negotiations.