Iranian security forces Sunday detained three more environmental activists on spying charges.
The detention came weeks after the first wave of arrests and the death in detention of an Iranian-Canadian head of a wildlife group took place.
"Three people were recently arrested in (southern) Hormozgan province. I cannot legally give details now ... but there is no doubt that infiltration by the United States and Israel is a serious matter," said judiciary spokesman Gholamhossein Mohseni Ejei, quoted by the semi-official Fars news agency.
After the earlier arrests, Iranian officials said the activists were gathering sensitive information under the guise of scientific and environmental activities.
The latest arrests come after the death of Kavous Seyed-Emami, an Iranian-Canadian environmental activist and sociology professor, who was arrested on January 24 and died in prison two weeks later.
However, the judiciary said Seyed-Emami, 63, had committed suicide.
The Center for Human Rights in Iran (CHRI), said at least nine other staff members and executives of Seyed-Emami's organisation had been arrested on the same day as him.
President Hassan Rouhani, a pragmatic cleric who defeated anti-Western hardliners to win re-election last year, has called for improving Iran's international ties and reforming the economy.
Human rights activists have reported that at least six detainees have died in prisons in the last two months in Iran but the judiciary, however, confirmed that three deaths took place in custody and all three were suicides.