A British-Iranian woman jailed in Tehran since June was arrested for having contacts with the "opposition based abroad" and propaganda offences against the regime, a justice official said on Tuesday.
Ghoncheh Ghavami, 25, was detained outside a stadium in the capital where she had gone to watch a volleyball match.
She was refused entry as women are not allowed to watch male athletes in the Islamic republic.
The law graduate, from London, was initially released after a few hours, but was rearrested days later at a police station where she had gone to reclaim items that had been confiscated near the stadium.
Ghavami's family and supporters say she was held for trying to watch the match, and on November 2 her lawyer said she had been tried and sentenced to one year in jail for propaganda offences against the regime.
However, the judiciary later denied the report of her sentencing and said the case remains under investigation.
On Tuesday, a statement by the Tehran prosecutor's office said evidence of Ghavami's anti-regime activities had been found on her mobile phone.
"After investigation, it seems she had participated in propaganda against the regime, had links with satellite TV channels, including BBC Persian, and the opposition based abroad and participated in demonstrations against the regime," the statement, published by state media, said.
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Iran bars contact with Farsi-language media such as BBC Persian and Voice of America, which are seen as vehicles of Western imperialism and opposition to the Islamic republic.
Despite the ban, illegal satellite dishes allow many Iranians to access such services.
The prosecutor's statement said Ghavami's mobile phone contained "numerous photos and videos related to the elements of sedition," a term used by authorities to describe the 2009 protests against the controversial re-election of president Mahmoud Ahmadinejad.
Ghavami's arrest "is not linked to her presence at a stadium where she wanted to watch a volleyball match", the statement added.
On November 11, Hadi Sadeghi, deputy chief of the judiciary's cultural affairs department, said Ghavami was arrested for having "acted against the security of the country and for links with foreigners".
The British Foreign Office raised concerns after Ghavami's reported sentencing, questioning "grounds for this prosecution, due process during the trial and Miss Ghavami's treatment while in custody".
Ghavami family members have said that at least 41 days of her detention before trial were spent in solitary confinement.
The case comes as Iran is under pressure over its human rights record, after a modest easing of its international isolation with moderate Hassan Rouhani's election last year as president.
Questioned about increasing executions and detentions under his rule, Rouhani has said the judiciary is independent of his government.