Iran will “descend like lightning” to avenge the death of a nuclear scientist, an adviser to the country’s supreme leader said.

The Iranian scientist that Israel alleged led the Islamic Republic’s military nuclear programme until its disbanding in the early 2000s was killed in a shootout on Friday, Iran’s state television said.

Hossein Dehghan, who is a presidential candidate in Iran’s 2021 election as well as an adviser to its supreme leader, echoed an earlier claim that Israel was behind the attack and issued a warning.

“In the last days of their gambling ally’s political life, the Zionists seek to intensify and increase pressure on Iran to wage a full-blown war,” Mr Dehghan wrote, appearing to refer to US President Donald Trump’s last days in office.

“We will descend like lightning on the killers of this oppressed martyr and we will make them regret their actions!”

Tehran’s foreign minister Mohammad Javad Zarif had suggested Israel was behind the attack, in which he said “Terrorists murdered an eminent Iranian scientist”.

“This cowardice — with serious indications of Israeli role — shows desperate warmongering of perpetrators,” Mr Zarif tweeted.

“Iran calls on int’l community—and especially EU—to end their shameful double standards & condemn this act of state terror.”

Israel declined to immediately comment on the killing of Mohsen Fakhrizadeh, who Israeli prime minister Benjamin Netanyahu once mentioned in a news conference saying: “Remember that name”.

Israel has long been suspected of carrying out a series of targeted killings of Iranian nuclear scientists nearly a decade ago.

State TV Friday cited sources confirming the death.

It said it would offer more information shortly.

Iran’s mission to the UN, meanwhile, described Fakhrizadeh’s recent work as “development of the first indigenous COVID-19 test kit” and overseeing Tehran’s efforts at making a possible coronavirus vaccine.

The semi-official Fars news agency, believed to be close to the country’s Revolutionary Guard, said the attack happened in Absard, a small city just east of the capital, Tehran.

It said witnesses heard the sound of an explosion and then machine gun fire.

The attack targeted a car that Mr Fakhrizadeh was in, the agency said.

State television on its website later published a photograph of security forces blocking off the road.

Mr Fakhrizadeh led Iran’s so-called Amad, or Hope programme.

Israel and the West have alleged it was a military operation looking at the feasibility of building a nuclear weapon in Iran.

Tehran long has maintained its nuclear programme is peaceful.

Mr Trump, who imposed sanctions on Iran this year, has been vocally critical of the nuclear programme. On Friday, he posted three re-tweets about the case without comment, including one in Hebrew.

The International Atomic Energy Agency says that Amad programme ended in the early 2000s.

IAEA inspectors now monitor Iranian nuclear sites as part of Iran’s now-unravelling nuclear deal with world powers.