Iranian President Hassan Rouhani has accused Israel of assassinating Mohsen Fakhrizadeh, the Islamic country's prominent scientist.

"Once again, the wicked hands of the global arrogance, with the usurper Zionist regime as the mercenary, were stained with the blood of a son of this nation," Rouhani said in a statement on his official website on Saturday, referring to Fakhrizadeh's killing. "The assassination of martyr Fakhrizadeh shows our enemies' despair and the depth of their hatred... His martyrdom will not slow down our achievements."

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Rouhani said Israel aims to create "chaos" by carrying out the scientist's assassination and that Iran will retaliate at "the proper time."

The office of Israeli Prime Minister Benjamin Netanyahu has said it would not comment on the attack. But revelations that Netanyahu once mentioned Fakhrizadeh in a 2018 news conference, saying "remember that name," has fueled speculation of the country's involvement.

Khamenei vows 'punishment' for assassins

Iranian authorities have threatened to avenge the death of Fakhrizadeh, who was gunned down in his car near Tehran on Friday.

Supreme Leader Ayatollah Ali Khamenei has called for "following up on this crime and certainly punishing the perpetrators and those responsible." He also urged the continuation of "the scientific and technical efforts of this martyr in all of the fields he was working in," according to a statement on his official website on Saturday. The sentiments were also echoed in a post on Twitter. 

Earlier Saturday, Israel raised the level of alert at its embassies around the world in the face of a possible revenge attack, according to Channel 12's N12 website.

Guido Steinberg, a Middle East expert from the German Institute of International and Security Affairs, told DW that he expects Tehran to make good on its threat.

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"We know that the Iranians retaliate. That's part of the reason why in 2012, the Israelis stopped their campaign of targeted killings — simply because the Iranians attacked Israeli civilians," he said. "[However] Israel, the United States and other governments are fighting hard against Iranian hit squads abroad, and their options are limited. I don't think that it's possible for the Iranians to successfully attack Israeli embassies."

Setback to diplomatic efforts

Fakhrizadeh's assassination could provoke confrontation between Tehran and Washington in the last weeks of Donald Trump's presidency.

US President-elect Joe Biden, who is set to take office in January, has promised to mend ties with Iran through diplomacy after four years of Trump's hawkish stance.

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Trump withdrew from the Iran nuclear deal in May 2018, accusing the Islamic Republic of using nuclear technology to build weapons of mass destruction. In January, a US airstrike killed Iran's top military commander Qassem Soleimani, with Trump threatening Iran with more actions.

Fakhrizadeh was the subject of US sanctions in 2008 for "activities and transactions that contributed to the development of Iran's nuclear program."

UN, Germany and Turkey urge restraint

Germany urged all sides to show restraint over the killing and to avoid escalating tensions that could derail any talks on Iran's nuclear program.

"A few weeks before the new US administration takes office, it is important to preserve the scope for talks with Iran so that the dispute over Iran's nuclear program can be resolved through negotiations," a Foreign Ministry spokesman said in an emailed statement. "We, therefore, urge all parties to refrain from any steps that could lead to a further escalation of the situation."

The United Nations spokesman issued a similar statement: "We urge restraint and the need to avoid any actions that could lead to an escalation of tensions in the region," adding that: "We condemn any assassination or extrajudicial killing."

Later on Saturday, Turkey also condemned Fakhrizadeh's killing, calling it a "heinous assassination."

The country’s foreign ministry called for the perpetrators to be held accountable and also urged "all sides to act with common sense and restraint."

Iran vows to continue Fakhrizadeh's path

Ali Akbar Salehi, the head of Iran's nuclear agency, has vowed that Fakhrizadeh's death will not stop the country's nuclear program.

"Fakhrizadeh's path is now being continued even more intensively," he said on Saturday.

Communications Minister Mohammad Javad Azari made a similar statement. "Thousands will grow back for the one flower that is torn out," he tweeted.

shs/mm (AFP, Reuters, dpa)

A previous version of this article stated that the Iran nuclear deal was signed in 2018. This has now been corrected. The department apologizes for the error.