The murder of Iran's top nuclear engineer would make it much harder for the U.S. president to resume negotiations between Tehran and Washington, a U.S.-based analyst said on Friday, just hours after the killing of Mohsen Fakhrizadeh.

As per the Iranian media sources that have not yet been fact-checked by NBC News, Mohsen Fakhrizadeh, labeled as the 'father of the Iranian bomb,' perished from injuries when gunmen fired shots at his vehicle.

An executive vice president of the Quincy Institute, a think-tank in Washington, DC, Trita Parsi, reported that the murder of Fakhrizadeh, a high-ranking nuclear engineer and leader of the Iranian Defense Ministry's Research and Innovation Agency, provided a "win-win" condition for Israeli Prime Minister Benjamin Netanyahu.

Parsi stated that Netanyahu might bring Washington into a military conflict with Tehran if the Iranian government reacts. Meanwhile, if Iran demonstrates restraint, the Israeli president could establish an environment that makes it much harder for U.S. negotiation with Iran.

Israel, which has now been suspected of carrying out a series of deliberate executions of Iranian nuclear scientists for years, refused to speak on the murder of Fakhrizadeh immediately.

"A criminal act & highly reckless"

Trump has not responded publicly on the murder of Fakhrizadeh on Friday. However, the U.S. president retweeted Israeli author Yossi Melman, who said that the murder of the nuclear engineer "is a major psychological and professional blow for Iran."

Nevertheless, top former and current United States authorities openly expressed doubts, particularly former CIA director John Brennan, who labeled the assault "a criminal act & highly reckless."

Brennan tweeted: "Iranian leaders would be wise to wait for the return of responsible American leadership on the global stage & to resist the urge to respond against perceived culprits."

Democratic Senator Chris Murphy had this to say: "Every time America or an ally assassinates a foreign leader outside a declaration of war, we normalize the tactic as a tool of statecraft." He also mentioned that he had not been made aware of the murder of Fakhrizadeh.

The murder happens at a "combustible" time, said Aaron David Miller, a senior officer at the Carnegie Endowment for International Peace.

More provocations?

Whereas the murder of Fakhrizadeh had been surprising to many in the sense of current Iran-U.S. affairs, director of the Center for Middle East Studies at the School of International Studies at the University of Denver, Nader Hashemi, stated that it "fits a pre-existing pattern."

Hashemi compared the murder of Fakhrizadeh to the United States assassination of top Iranian military officer Qassem Soleimani, who has been assassinated on January 3 nearby Baghdad's airport terminal.

No reason for a U.S. strike

Several sources had stated that the U.S. armed forces' opinion at the moment is that there is no reason for a U.S. attack until there is a clear threat by Iran against the United States. The military task of reaching a target like Natanz's nuke plant stays consistent. 

It would take frequent armed airstrikes and air defenses to get through Iran, and the United States thinks Iran would quickly counter in the field with missile attacks.

These accounts argue that there would have to be a clear and distinctive threat to cause a U.S. military intervention.