Antony J. Blinken is in the middle of his most intense trip as the top American diplomat, traveling to at least seven countries across the Middle East in four days to shore up support for Israel as it wages war against Hamas.

During a whirlwind tour, at times guarded by security officers wearing body armor, the secretary of state broadcast several U.S. messages at once. He made clear that the United States fully supports Israel’s counterattack in response to Hamas’s cross-border incursion, which killed more than 1,300 people.

He sought to persuade Arab countries to limit their criticism — no easy task as devastating Israeli strikes have killed about 1,900 Palestinians, according to the Palestinian Health Ministry.

Mr. Blinken and his top aides also spoke with their hosts about efforts to free hostages Hamas was holding in Gaza, including what U.S. officials say may be some American citizens abducted from Israel on Saturday. And he tried to ensure that the conflict did not widen to draw in other enemies of Israel, such as Iran or the Lebanon-based militia Hezbollah.

Mr. Blinken landed in Israel on Thursday, less than one week after Hamas gunmen attacked towns in the southern part of the country.

Defense Secretary Lloyd J. Austin III arrived in Tel Aviv a day later, with a similar message of support.

After a swing through Jordan, Qatar, Bahrain and Saudi Arabia on Friday, Mr. Blinken plans to carry on to the United Arab Emirates and Egypt.

His travels come as the Israel-Palestinian conflict reaches a degree of violence not seen in many years and poses myriad new challenges for President Biden’s foreign policy, which has been focused on defending Ukraine and countering Chinese power.

Mr. Blinken’s travels reflected a tension for the Biden administration. Likening the atrocities committed by Hamas to those of the Islamic State, Mr. Biden and Mr. Blinken aim to send a clear message that the United States largely supports Israel’s actions in Gaza and that countries in the region should do the same.

“Israel has both the right and even the obligation to defend its people,” Mr. Blinken said at a news conference in Doha, Qatar. “What Israel is doing is not retaliation. What Israel is doing is defending the lives of its people,” and, he added, “trying to make sure that this cannot happen again.”

“Imagine if this happened in the United States,” he said.

At the same time, Mr. Blinken signaled, albeit more gently and in terms that can sound pro forma, some concern about the potential impact on Gaza’s largely impoverished Palestinian population of two million

“But at the same time,” he said in Doha, “the way Israel does this matters.” Mr. Blinken said he had spoken with Israeli officials about the need to ensure civilians were not harmed.

He then added that Hamas “uses civilians as human shields” — a line that suggests an understanding that Israeli attacks will necessarily involve many innocent casualties.

Biden administration officials understand that although Israel has been showered with international good will this week, criticism will rise among Americans and citizens of other countries as it carries out what it says will be a long military offensive in Gaza.

Even so, Mr. Blinken signaled in his travels that the Biden administration would have a high tolerance for whatever results from Israel’s military response.

During his first stop, at a military base in Tel Aviv where diplomatic security officials who typically wear suits donned camouflage military gear, Mr. Blinken delivered the message directly to Prime Minister Benjamin Netanyahu of Israel: “We will always be there by your side.”

“Too often in the past, leaders have equivocated in the face of terrorist attacks against Israel and its people,” Mr. Blinken said. “This is — this must be — a moment for moral clarity.”

Mr. Blinken is carrying that message to the Arab nations he is visiting through Sunday. Of those countries, only the United Arab Emirates and Bahrain have explicitly condemned Hamas for its attacks.

Qatar’s first statement after the attacks said Israel was “solely responsible” for the violence against its citizens because of its blockade of Gaza. Saudi Arabia issued a statement making a similar case.

In a statement on Friday, the government of Jordan said the country’s monarch, King Abdullah, had pressed Mr. Blinken on the need for humanitarian corridors and aid into Gaza, and “warned of inflicting collective punishment against Gaza residents.” It contained no condemnation of Hamas.

Such talk highlights the challenges for Mr. Blinken among the Arab nations. But it also belies the private unease that many Arab leaders have with Hamas, said Dennis Ross, who was a Middle East adviser to several presidents and now is with the Washington Institute for Near East Policy.

Mr. Blinken’s challenge, he said, “is to remind everybody that Hamas can’t be seen as winning. Hamas must been seen as decisively losing.”

“Everyone he sees in private, they are going to agree,” Mr. Ross said.

Mr. Blinken has also pursued two other key goals on his trip.

One is for nations in contact with Hezbollah and Iran to tell them not to join the war. The other is for countries that have influence with Hamas to help win the release of the 150 or so hostages taken on Saturday. Mr. Blinken was accompanied on his trip by Steve Gillen, the U.S. deputy special envoy for hostage affairs, who remained in Israel after his departure.

Mr. Biden joined a call on Friday with Mr. Gillen’s boss, Roger Carstens, the special envoy for hostage affairs, and other top officials including the national security adviser, Jake Sullivan, White House officials said.

Qatar is a crucial interlocutor, making Mr. Blinken’s stop there especially sensitive. Officials in Doha speak to Iran, host offices for leaders of Hamas and have mediated hostage and prisoner releases in the Middle East and Afghanistan.

“I’m grateful for the urgency that Qatar is bringing to this effort,” Mr. Blinken said at a news conference on Friday in Doha with the prime minister and foreign minister of Qatar, Mohammed bin Abdulrahman bin Jassim Al Thani.

Asked by a reporter whether his government would continue to allow Hamas to operate in Doha, a subject of sharp criticism from supporters of Israel, Mr. Al Thani called the office useful “as a way of communicating and of bringing peace and calm to the region.”

In language clearly directed at Israel, Mr. Al Thani also said that Qatar opposes “collective punishment” and “hitting and targeting civilians, women and children.”

In Qatar, Mr. Blinken did not publicly address the subject of Hamas’s presence in the country, though he did say in general terms that, after Saturday’s “unconscionable” attacks, “there can be no more business as usual with Hamas.”

“You can expect that he was probably much more blunt in private,” Mr. Ross said.

In a planned stop in Saudi Arabia’s capital of Riyadh, Mr. Blinken is expected to discuss how the conflict could affect months of negotiations in search of an agreement that might officially normalize relations between Israel and Saudi Arabia. The deal would include U.S. concessions to Riyadh such as a security agreement.

Since the Hamas attacks and the start of Israel’s military campaign against Palestinians, Saudi officials have adopted a wait-and-see posture before moving forward with the normalization talks. John F. Kirby, a spokesman for the National Security Council, told reporters on Friday that the United States still supported a Saudi-Israel agreement.

“But obviously, these are sovereign nations,” he added. “They get to decide for themselves at what pace they’re willing to move, under what conditions — and certainly the degree to which they want to continue that effort.”

During his visit to Israel, Mr. Austin met with Israeli leaders and also reaffirmed U.S. support for their new offensive against Hamas.

Mr. Austin arrived from Brussels, where he was attending a NATO defense ministers meeting. He got a firsthand look at some of the weapons and security aid that the Biden administration has rushed to Israel after last weekend’s attack. A second shipment of arms arrived on Friday, Israeli officials said.

Asked about the likelihood of civilian casualties in Gaza as Israeli troops prepare to mount a major ground assault there, Mr. Austin said Israel has the right to defend itself. He added that he has worked with Israeli forces over the years, when he was a top Army general.

“They are professional, they are disciplined and they are focused on the right things,” he told reporters after meeting for nearly two hours with his Israeli counterpart, Yoav Gallant, and the Israeli war cabinet.

Eric Schmitt contributed reporting from Washington.