President Hassan Rouhani blamed Israel for the killing.

Israel has stayed silent.

It had previously accused Mohsen factories are day of being behind a secret nuclear weapons program.

Our correspondent, Paul Adams, has more God angry protests Once mawr on the streets of the Iranian capital, people here in no doubt about who was behind Friday's killing, the father of Iran's nuclear program is now being treated like a martyr.

His assassination, the subject of headlines and debate attacks like this have happened before.

10 years ago, Israel carried out a campaign which killed four other nuclear scientists.

But the death of most in fact, Louzada poses a dilemma for Iran's leadership.

Retaliate or bide their time, the supreme leader, Ali Khamenei, said the perpetrators on those who commanded them will be pursued and punished.

But Iran knows the next American president wants dialogue, not confrontation.

Hence a more cautious response from the country's pragmatic president thinks savage act shows that our enemies feel that global conditions are changing and it's important for them to make the most of the remaining few weeks that they have to create uncertain conditions in the region, but our brave nation is smarter than to fall into the trap of Zionists.

But pressure is mounting.

Iran has yet to retaliate for the death of Qasem Soleimani, killed by a U.

S drone strike in January.

Iran's recent progress in its nuclear program may have triggered this attack, a stark warning to Iran's entire nuclear establishment.

But it's also likely to make Joe Biden's difficult job coaxing Iran back into negotiations that much harder.

Paul Adams, BBC News.