The American website "Axios" said that three American officials confirmed to the website that the Biden administration is convinced that Iran will attack Israel in response to the assassination of Hamas political leader Ismail Haniyeh in Tehran on Wednesday and is preparing to confront it, while American press reports stated that the United States is preparing to send additional fighters to the Middle East.

U.S. officials say they expect any Iranian retaliation to be similar in style to its April 13 attack on Israel — but perhaps broader in scope — and could also include the involvement of Lebanon's Hezbollah.

Iranian Supreme Leader Ayatollah Ali Khamenei and senior Iranian political and military officials have confirmed in statements that Iran will respond to Haniyeh's assassination.

Hezbollah leader Hassan Nasrallah also vowed to respond to the Israeli airstrike in Beirut on Tuesday, which assassinated the head of the party's operations room.

The Biden administration fears that it will be difficult to muster the same international and regional coalition of countries that defended Israel from the previous Iranian attack, because Haniyeh’s assassination comes in the context of the war between Israel and Hamas, which has stirred anti-Israel sentiment across the region.

Axios reported that Biden and his top aides are frustrated by the current situation, and fear that it will be difficult to mobilize an international and regional coalition similar to the one that helped Israel repel the previous Iranian attack last April, according to the website.

The New York Times quoted American officials as saying that Washington is preparing to send additional fighter jets to the Middle East to confront current threats.

The Iranian attack in April came in response to an Israeli air strike that targeted the Iranian consulate in Damascus, killing a senior Iranian general.

An American official said that the "American intelligence community" began receiving clear indications on Wednesday that Iran would respond to the assassination of Haniyeh in Tehran, while two American officials said that it might take the Iranians and their proxies a few days to coordinate and prepare an attack on Israel.

Another US official said the Pentagon and US Central Command were making preparations similar to those they did before the attack in April.

"The official said that the preparations include US military assets in the Gulf, the eastern Mediterranean and the Red Sea," adding, "We expect a few difficult days," according to the website.

The website quotes a senior Israeli official as saying that Israeli intelligence expects Iran to launch a large-scale missile attack on Israel.

It is noteworthy that the Israeli army spokesman, Daniel Hagari, said in a press briefing on Thursday, that "Israel's international partners have reinforced their forces in the region in order to help confront any possible attack."

White House National Security Adviser Jake Sullivan said in a briefing with reporters on Thursday that the risk of a wider war in the Middle East remains today.

He pointed out that the Biden administration is making intensive efforts to deter any wider war and calm the situation through diplomacy.

Speaking at the funeral of his top military adviser, Fouad Shukr, Hezbollah Secretary-General Hassan Nasrallah said on Thursday that the party would carry out a major response against Israel in the coming days.

Nasrallah also said he expected Iran to respond to Haniyeh's assassination, as well as "parties of the axis of resistance" in Iraq and Yemen.

"We are not talking about separate fronts anymore. This is an open campaign on all fronts and there is no doubt that [the war] has entered a new phase," he added.

Several US and international airlines, including United, Delta, Lufthansa and Swiss, have announced the suspension of flights to and from Israel.

According to the website, "the Israeli army is on high alert in anticipation of a possible retaliatory response from Iran and Hezbollah. Prime Minister Benjamin Netanyahu held a meeting on Thursday to assess the readiness of the Home Front Command in the Israel Defense Forces."