Top Iranian official says Israel used "electronic devices" to remotely kill Mohsen Fakhrizadeh who was laid to rest in a cemetery in northern Tehran.
Iran has laid to rest a nuclear scientist in a funeral befitting a "martyr", with a top Iranian security official accusing Israel of using "electronic devices" to remotely kill Mohsen Fakhrizadeh who founded the country's military nuclear programme in the 2000s.
The official also accused an opposition group of being behind the attack.
State television showed several high-ranking Iranian officials mourning the nuclear scientist's death at the ceremony on Monday, including Defence Minister Amir Hatami and the head of the Revolutionary Guards Hossein Salami.
Fakhrizadeh died on Friday from his wounds after his car was ambushed outside the capital, heightening tensions once more between Tehran and its foes.
Ali Shamkhani, Secretary of the Supreme National Security Council of Iran, told state TV: "This was a very complicated assassination that was carried out remotely with electronic devices."
"We have some clues but surely the 'Monafeghin' group was involved and the criminal element behind it is the Zionist regime (Israel) and Mossad," he added, referring to Israel's foreign intelligence service.
"Monafeghin" is a term officials employ to refer to the Paris-based National Council of Resistance of Iran (NCRI), an umbrella bloc of opposition groups in exile that seek an end to Shia Muslim clerical rule.
The New York Times has reported an American official and two other intelligence officials confirmed Israel was behind the attack, without giving further details.
Tehran to double nuclear research wing budget to honour Fakhrizadeh
The funeral, held at the ministry, got underway with a religious singer praising Fakhrizadeh and alluding to the martyrdom of Imam Hossein, the revered seventh-century holy figure from whom Shia Muslims draw inspiration.
"If our enemies had not committed this heinous crime and spilt our dear martyr's blood, he might have remained unknown," Hatami said in a speech.
"But today, he who was only an idol for [...] his students and colleagues, is introduced to the whole world," he added, saying he will be an inspiration for "all who embark on the path to fight."
"The enemies should know, that this is their first defeat."
Hatami had said after the scientist's death that Fakhrizadeh was one of his deputies and headed the ministry's Defence Research and Innovation Organization, focusing on the field of "nuclear defence."
In his speech, he said the government has decided to double the organisation's budget to continue Fakhrizadeh's path "vigorously."
A large display showed a picture of Fakhrizadeh next to Iran's supreme leader Ayatollah Ali Khamenei, as well as former top general Qasem Soleimani, who was killed in a January air strike by the US in Baghdad.
At around 0800 GMT, the scientist's coffin was being buried at Imamzadeh Saleh, an important Shia shrine in northern Tehran where two other slain nuclear scientists were buried in 2010 and 2011.
Israel's alleged role in assassinating scientists
Israel, long suspected of killing Iranian nuclear scientists over the last decade, has declined to comment on the attack.
Fakhrizadeh headed Iran's so-called Amad programme, 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 programme" ended in 2003. US intelligence agencies concurred with that assessment in a 2007 report.
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 its nuclear programme is peaceful.
Media report evidence
Shamkhani's remarks drastically change the story of Fakhrizadeh's killing on Friday.
Authorities initially said a truck exploded and then gunmen opened fire on the scientist, killing him.
State TV's English-language Press TV earlier reported a weapon recovered from the scene of the attack bore "the logo and specifications of the Israeli military industry."
State TV's Arabic-language channel Al-Alam claimed the weapons used were "controlled by satellite," a claim also made on Sunday by the semi-official Fars news agency.
"Unfortunately, the operation was a very complicated operation and was carried out by using electronic devices," Shamkhani told state TV.
"No individual was present at the site," he added.