Iran said Thursday an engineer was killed in an "accident" at a defence research unit in an area near Tehran that hosts a military complex previously scrutinised by the UN nuclear watchdog.
The incident late Wednesday came days after a colonel in the Revolutionary Guards, the ideological arm of Iran's military, was shot dead near his home in east Tehran.
Iran's arch foe Israel told the United States it was behind the operation, The New York Times reported. Iranian officials had blamed agents of the US and its allies for the "assassination", the most high profile inside Iran since 2020.
On Thursday, Guards commander Hossein Salami said that the killing "will be responded to... Our enemies should wait," without naming who they were.