Iran has released six of eight Slovak paragliders held since May for alleged spying, Slovak Prime Minister Robert Fico said Sunday.
"Negotiations with Iran were very correct and led to the release of six out of eight Slovak citizens," Fico told journalists.
"Two Slovaks are still held in Iran until further allegations are investigated by the Iranian authorities," he said, saying he expected further negotiations to be "extremely complicated."
In July, Iran's judiciary said it was probing nine people -- one Iranian and eight Slovaks -- arrested for "illegal activities, including photographing restricted areas" in the central Isfahan province, which is home to nuclear facilities including the Natanz uranium enrichment site.
Isfahan is located some 330 kilometres (200 miles) south of the capital Tehran.
The international community has imposed a battery of sanctions against Iran, accusing it of using its civilian nuclear energy programme as a cover for developing atomic weapons -- charges Tehran flatly denies.
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Friends of the paragliders told AFP they were not spies, but were travelling to film documentaries from a bird's-eye view.
They said the men were in Iran to collect material for a second film, after making a documentary last year on paragliding over the Himalayas.
Senior Iranian prosecutor Gholam Hossein Mohseni Ejeie asserted the men had smuggled in unspecified "equipment."
The paragliders ran into trouble for using two-band walkie talkies reportedly banned in Iran, as well as cameras designed for extreme sports.
"As far as we know, it's prohibited to take pictures in Iran while flying lower than 2,300 metres (7,545 feet). We only took pictures from a higher altitude," Vladislav Frigo, one of the released paragliders told journalists.
Frigo conceded the group had two-band walkie talkies, which are banned in Iran, but said "we didn't use the prohibited band."
According to Frigo, those arrested were held in one big cell with a TV set and a small corner kitchen, separated from other prisoners.
"It was bearable, the prison staff and investigators treated us very nicely," Frigo said.