Hassan Firuzabadi, senior military advisor to supreme leader Ayatollah Ali Khamenei, was responding to questions from local media on the recent arrest of environmentalists.
He said he did not know the details of the cases, but that the West had often used tourists, scientists and environmentalists to spy on Iran.
"Several years ago, some individuals came to Iran to collect aid for Palestine... We were suspicious of the route they chose," he told the reformist ILNA news agency.
"In their possessions were a variety of reptile desert species like lizards, chameleons... We found out that their skin attracts atomic waves and that they were nuclear spies who wanted to find out where inside the Islamic republic of Iran we have uranium mines and where we are engaged in atomic activities," he said.
His comments came after news that a leading Iranian-Canadian environmentalist, Kavous Seyed Emami, had died in prison after he was arrested along with other members of his wildlife NGO last month.
The deputy head of the Environmental Protection Organisation, Kaveh Madani, was also reportedly detained temporarily over the weekend.
Firuzabadi said Western spy agencies have "failed every time".
He said another espionage case involved a couple from Germany.
"They got them on a fishing boat from Dubai and Kuwait and sent them to the Persian Gulf to identify our defence systems," he said.
"But when we arrested them, they said they had come for fishing and were tourists."
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