Iran has arrested some of those responsible for assassinations of its nuclear scientists, state media reported on Sunday.

Intelligence Minister Heydar Moslehi said Iran had shut down two networks inside and outside the country he said were involved in training the killers, the Fars news agency reported.

At least four scientists associated with Iran’s disputed nuclear program have been slain since 2010. A fifth, Fereydoun Abbasi Davani, now the head of Iran’s Atomic Energy Organization, was wounded.

In the most recent case, a magnetic bomb attached to a car killed nuclear scientist Mostafa Ahmadi Roshan in January.

Moslehi did not say how many people had been arrested, for which killings they were allegedly responsible, where the networks were operating or how they trained the assassins.

“They (the two networks) took steps not to leave any clues behind but they were stricken by mistakes,” he said.

Reuters reported that Moslehi spoke at a ceremony marking the first anniversary of the shooting death of Dariush Rezainejad, saying, “We were able to arrest the main actors in this act of terrorism.”

Iran blamed the U.S., Britain and Israel for the killings of the five scientists, but the U.S. and Britain denied involvement. Israel has not commented.

Earlier this month, Moslehi accused French and German intelligence services of cooperating with the CIA to kill Iranian nuclear scientists.

In May, Iran hanged a man the regime alleges was an agent for the Israeli Mossad and convicted of killing one of its nuclear scientists in 2010.