Tehran blamed Israel for the death last week of Iranian nuclear research scientist Mostafa Ahmadi Roshan, who was killed in a car bomb attack in north Tehran.
Roshan's death follows heightened diplomatic and economic pressure from Western allies convinced Iran is working on technology that could be used to build a nuclear bomb. Tehran maintains its nuclear program is for peaceful purposes.
Iran's Ayatollah Ahmad Jannati said in a sermon following Friday prayers that the assassination was an act of desperation.
"This assassination was planned and carried out with the help of the CIA and Mossad and shows that the global arrogance, led by the U.S. and Zionist (Israel), has reached a dead end when it comes to the pious, determined and progressive Iranian nation," he was quoted by Iran's state-funded broadcaster Press TV as saying.
Foreign ministers from European countries next week are expected to consider expanding sanctions against Iran in a package that includes an oil embargo and restrictions imposed on the Iranian financial sector.
The report from Press TV adds that Roshan met recently with inspectors from the International Atomic Energy Agency, "a fact which indicates the U.N. nuclear agency may have leaked information about Iran's nuclear facilities and scientists."