The West believes Iran is stockpiling enriched uranium as potential fuel for nuclear weapons and trying to develop technology needed for a workable bomb. Iran denies this, saying its nuclear activity is solely for peaceful energy purposes.

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.

Moslehi spoke at a ceremony marking the first anniversary of the shooting death of Dariush Rezainejad. Initial reports in Iranian media suggested Rezainejad was involved in Iran’s nuclear program, but later said he was an engineering student.

“We were able to arrest the main actors in this act of terrorism,” Moslehi was quoted as saying.

Iran blames the assassinations on U.S., Israeli, French, British and German spy agencies, especially the Israeli Mossad.

In May, Iran hanged 24-year-old Jamal Fashi for the murder of scientist Massoud Ali-Mohammadi in January 2010, saying that Fashi had gone to Israel for training.

The United States has denied any role in the killings. Israel has remained silent.

Sporadic talks between six world powers and Iran to defuse the decade-long stand-off over its nuclear ambitions have so far failed to yield a breakthrough.

A European Union ban on the import, purchase or shipping of Iranian oil took effect on July 1 as part of widening international sanctions aimed at prodding Tehran into curbing enrichment and opening up to U.N. nuclear inspections.

Meanwhile, Iran’s atomic chief on Sunday undercut an idea put forward by some lawmakers to make nuclear-powered submarines and ships, even though he claimed Tehran had the technology to do so later if it wished.

The comments by head of Iran’s Atomic Energy Organization as reported by the news agency ISNA, poured cold water on a recent draft bill by some Iranian parliamentarians that seeks to give Tehran a reason to produce high-enriched uranium.

“We don’t have a plan right now in this area,” Davani was quoted as saying.

He asserted, though, that “we do have the ability to design such reactors for ships” if a decision was made to go in that direction.
Enrichment is at the heart of the showdown between Iran and the West over Tehran's nuclear program.

Iranian lawmakers signaling their defiance in the face of the pressure floated the idea of their country making nuclear-powered submarines and freighters in what observers took to be an attempt to raise the stakes in the talks.

This month, several lawmakers entered a bill calling on the government to prepare the way for Iran to make nuclear-powered commercial ships -- a technological feat seen as both uneconomical and beyond the ability of all but the world's most-advanced nuclear states.

“If it’s necessary and the government so decides, we have no problem to advance towards such systems and technologies,” Davani was quoted as saying.

He said that, in the case of ships, “it’s not necessary to have fuel (enriched) beyond 20 percent -- there are reactors that work with 3.5 percent or five percent in ships.... But if it's for submarines... higher enriched uranium is needed.”

But, he repeated: “Right now, we have no plan to do so. Currently, fuel production to 20 percent is carried out for the Tehran reactor and for another similar reactor we are planning to build.”

He also said that “ships with nuclear fuel have environmental problems.”

If a decision were ever made to proceed with ship-board nuclear reactors, Abbasi Davani added, “we will hold the necessary coordination with the IAEA,” the U.N.’s nuclear watchdog.