Iran’s President Hassan Rouhani on Monday claimed that Israel was behind the killing of a scientist who founded the Islamic Republic’s military nuclear program in the 2000s in an effort to start a war in the last days of President Trump's administration.

Rouhani's comments in a news conference marked the first time he has directly accused the Jewish state of carrying out the killing of Mohsen Fakhrizadeh late last month.

Israel, long suspected of killing Iranian nuclear scientists over the last decade, has repeatedly declined to comment on the attack.

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“Waging instability and war in the final days of the Trump administration was the main aim of the Zionist regime in the assassination,” Rouhani said.

In this photo released by the official website of the office of the Iranian Presidency, President Hassan Rouhani speaks during his press conference in Tehran, Iran, Monday, Dec. 14, 2020. Rouhani on Monday claimed that Israel was behind the killing of a scientist who founded the Islamic Republic’s military nuclear program in the 2000s in an effort to start a war in the last days of President Trump's administration. (Iranian Presidency Office via AP)

In this photo released by the official website of the office of the Iranian Presidency, President Hassan Rouhani speaks during his press conference in Tehran, Iran, Monday, Dec. 14, 2020. Rouhani on Monday claimed that Israel was behind the killing of a scientist who founded the Islamic Republic’s military nuclear program in the 2000s in an effort to start a war in the last days of President Trump's administration. (Iranian Presidency Office via AP)

Rouhani vowed to avenge the killing but said his country will not allow Israel to decide the “time or venue“ of any retaliatory action. He said Iran will not allow instability in the region.

Fakhrizadeh headed Iran’s so-called AMAD program, which Israel and the West have alleged was a military operation looking at the feasibility of building a nuclear weapon. The International Atomic Energy Agency says that “structured program” ended in 2003. U.S. intelligence agencies concurred with that assessment in a 2007 report.

After the killing of Fakhrizadeh, a top Iranian security official, Ali Shamkhani, accused Israel of using “electronic devices” to remotely kill the scientist.

Israel insists Iran still maintains the ambition of developing nuclear weapons, pointing to Tehran’s ballistic missile program and research into other technologies. Iran long has maintained that its nuclear program is for peaceful purposes.

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Rouhani also referred Monday to the 2015 nuclear deal between Iran and world powers, from which President Donald Trump removed the U.S. in 2018. “We believe the situation will be changed under the new U.S. administration," he said.

President-elect Joe Biden has said the U.S. could potentially return to the nuclear deal.

In November, Elliott Abrams, the U.S. special representative for Iran, insisted that a pressure campaign of sanctions targeting Iran would continue into the Biden administration.

Abrams said sanctions targeting Iran for human rights violations, its ballistic missile program and its regional influence would remain in place.

“The missile program and regional issues have no link to the nuclear deal,” said Rouhani. “These are not matters of discussion, at all.”

Rouhani also said the reaction of the European Union to Saturday's execution of Iranian journalist Ruhollah Zam, whose work helped inspire nationwide economic protests in 2017, was an “intervention” into Iran’s domestic affairs.

In this picture released by the Iranian Defense Ministry and taken on Saturday, Nov. 28, 2020, caretakers from the Imam Reza holy shrine, carry the flag draped coffin of Mohsen Fakhrizadeh, an Iranian scientist linked to the country's disbanded military nuclear program, who was killed on Friday, during a funeral ceremony in the northeastern city of Mashhad, Iran. An opinion piece published by a hard-line Iranian newspaper has suggested that Iran must attack the Israeli port city of Haifa if Israel carried out the killing of a scientist. (Iranian Defense Ministry via AP)

In this picture released by the Iranian Defense Ministry and taken on Saturday, Nov. 28, 2020, caretakers from the Imam Reza holy shrine, carry the flag draped coffin of Mohsen Fakhrizadeh, an Iranian scientist linked to the country's disbanded military nuclear program, who was killed on Friday, during a funeral ceremony in the northeastern city of Mashhad, Iran. An opinion piece published by a hard-line Iranian newspaper has suggested that Iran must attack the Israeli port city of Haifa if Israel carried out the killing of a scientist. (Iranian Defense Ministry via AP)

Iran on Sunday summoned the German and French envoys to Tehran after the European Union condemned the execution by hanging of Zam.

Rouhani said the case was handled according to the Iranian law. “A court has reviewed the case and issued the verdict. We do act in the framework of our regulations.”

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However, he said he believes the case would not harm Iran's relations with Europe. “ I see it as unlikely that the case will damage Iran and Europe relations.”

Zam, 47, had been imprisoned in Iran after Iranian authorities seized him while he was traveling in neighboring Iraq last year. He had been living in exile in France before that.

The German Foreign Ministry on Saturday expressed shock at the circumstances of Zam’s sentencing and what it described as his “abduction from abroad” and forced return to Iran.

“This is a barbarous and unacceptable act,” the French Foreign Ministry said in a statement, which condemned the hanging as a “grave blow” to freedom of speech in Iran.

Zam’s website, AmadNews, and a channel he created on the popular messaging app Telegram had reported the timings of the 2017 protests and embarrassing information about officials that directly challenged Iran’s Shiite theocracy.

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Zam is one of three opposition figures apparently detained in intelligence operations abroad in the last two years.