Iran's Intelligence Ministry on Sunday announced the arrests of at least 20 agents it said were behind the assassination of Iranian nuclear scientists, state news agency IRNA reported. After initially announcing a series of arrests last week, police tied the agents directly to Israel, alleging that they were "hired by an Israeli spy network."

According to IRNA, the arrests were carried out in multiple sting operations across the country. The agents were blamed specifically for the killings of Majid Shahriari, Mostafa Ahmadi Roshan and Reza Qashqaei - all scientists allegedly working on Tehran's contentious nuclear program.

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Iran initially announced the series of arrests of foreign agents last Thursday, after which it declared its commitment to continue efforts to bring to justice the "terrorists" who "martyred the young scientists in cold-blooded murder," IRNA reported.

The announcement marked the second wave of Iranian arrests of alleged assassins in recent months. In April, Iran said it arrested several members of a "major terrorist group" over the killing of nuclear scientists.

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Tehran has in the past accused Israel of being behind the killings of several of its nuclear scientists. In January, the Islamic state blamed Israel when a nuclear scientist was killed by a bomb placed on his car by a motorcyclist in Tehran.

Tensions are running high between Iran and Israel, which has not ruled out a military strike on the Islamic Republic if diplomatic efforts fail to resolve a row over Tehran's disputed nuclear program.

Reuters contributed to this story.