"We have discovered some clues and some arrests have been made," Larijani told the Arabic-language broadcaster.

Mostafa Ahmadi Roshan, a deputy director of Iran’s largest uranium enrichment plant, died in a car bomb explosion in Tehran last week. Local police sources said a passing motorcyclist attached a magnetic mine to the car Roshan was riding in.

Larijani did not give any further details on the arrests but vowed his country would avenge the death using "non-terrorist" tactics.

Iran's Supreme Leader Ayatollah Ali Khamenei has accused the U.S. and Israeli intelligence services of killing of the scientist.

The United States has already denied having anything to do with the Iranian scientist's murder. Israel has not commented on its alleged involvement in the assassination.

The attack was similar to several other attacks on Iranian nuclear scientists in the past two years.

In January 2010 Professor Mahsud Ali Mohamed of Tehran University was killed outside his home. Local police say he died when a motorcycle exploded next to his car as he got into the vehicle.

In November of that year, bomb attacks killed two atomic scientists, Majid Shakhriani, and his colleague Dr. Fereidoun Davani-Abbasi, and injured their wives. In both cases, their cars were attacked by unknown motorcyclists.

Western nations claim Iran’s nuclear energy research is a cover for atomic weapons production, which Tehran has consistently denied.

Iran recently began enrichment of uranium up to 20 percent at its Fordo facility as part of its nuclear program, the IAEA said on Monday. Russia said it was concerned by the move, which was condemned by the Western powers.