An Iranian government panel has concluded there is no evidence against environmental activists rounded up on spying charges in recent months, the country's environment chief says.

Isa Kalantari, head of Iran's department of environment, was quoted by state media as saying on May 22 that the conclusion had been reached by a panel set up to investigate the allegations against the activists.

The panel included the ministers of justice, interior, and intelligence, as well as the president's legal deputy, Kalantari said.

"This four-member group has come to the conclusion that these detained individuals are in custody without having done anything and naturally they must be freed soon," Kalantari said.

Iran detained several environmentalists and wildlife activists earlier this year on espionage charges. The total number of those arrested is not clear.

Judiciary officials claimed that the activists were gathering sensitive information for foreign governments under the guise of scientific and environmental activities.

Among those detained was Iranian-Canadian environmental activist and sociology professor Kavous Seyed Emami, who died in prison under disputed circumstances.

The judiciary said the 63-year-old managing director of the Persian Wildlife Heritage Foundation, which works to protect endangered animals and raise public awareness about the environment, had committed suicide in prison.

The claim has been questioned by his family and acquaintances.

Kalantari's deputy at the department of environment, Kaveh Madani, fled the country last month amid pressure from hard-liners.

Madani said last year he had returned to Iran "to create hope" and pave the way for the return of other expatriates.

Based on reporting by ISNA and AFP