Washington (CNN) -- Former U.S. Marine Amir Hekmati has been convicted in Iran by a secret court of "practical collaboration with the U.S. government" and sentenced to 10 years in prison, his sister told CNN on Friday.
The news follows a public campaign by Hekmati's family to win his release from Iran, where he has been held for nearly three years under Iran's claim that he was an American spy.
Hekmati's attorney, Mahmoud Alizadeh Tabatabaei, told The New York Times on Friday that client had never been informed about the retrial, conviction or sentence.
Tabatabaei told the newspaper he learned of the conviction during recent discussions with judiciary officials. He then telephoned to inform Hekmati, who has been held in Tehran's Evin prison, and with family members on the United States.
Hekmati, 30, has long maintained his innocence, saying he had gone to Iran to visit his grandmother when he was arrested in August 2011, and accused by Iran's Intelligence Ministry of working as a CIA agent.
Days before his arrest, Hekmati called his mother from Iran to say he would be coming home soon. He told them he would leave two days after a final farewell party his Iranian relatives were having on August 29.
Hekmati never showed up at the party.
For three months, no one in his family knew anything his whereabouts. Then one day in December 2011, Iranian state television aired Hekmati's purported confession that he was a CIA spy, and announced that he was imprisoned.
Hekmati wrote a letter to U.S. Secretary of State John Kerry saying a confession he made to the spying charges leveled by Iran were "false" and "based solely on confessions obtained by force, threats, miserable prison conditions, and prolonged periods of solitary confinement."
The initial charge and detention has stretched to a two-year ordeal. Weeks after his on-air confession broadcast on Iranian television, Hekmati was tried in an Iranian court and sentenced to death. Months later, Iran's Supreme Court overturned his death sentence and ordered a retrial.
During his imprisonment, Hekmati spent 16 months in solitary confinement and went on a month-long hunger strike.
Enlisted in the Marines
Hekmati was born in Arizona and raised in Flint, Michigan, after his parents emigrated from Iran. His parents came to the United States in 1979 as the Islamic revolution spread across Iran.
Hekmati joined the Marines after high school, and served four years, becoming a rifleman and also serving in Iraq.
Two years ago Hekmati surprised his parents by telling them he wanted to visit Iran for the first time, to meet relatives he had never seen -- including his ailing grandmother -- and find his roots.
The Hekmati family has tried to bring public attention to Amir Hekmati's plight, hoping to secure his release.
Other Americans detained
Hekmati is the latest American in recent years to face arrest and prosecution in Iran:
• In 2007, Iran arrested several Iranian-Americans -- including Kian Tajbakhsh, Ali Shakeri and Haleh Esfandiari, who were all later released. (That same year retired FBI agent Robert Levinson went missing after last being seen on Iran's Kish Island. Despite photos from his captors, his whereabouts are still unknown.)
• In May 2008, retired Iranian-American businessman Reza Taghavi was arrested on suspicion of supporting an anti-regime group. He was released more than two years later.
• In 2009, three U.S. hikers, also accused of spying, were arrested but ultimately released.
• Tajbakhsh was re-arrested in July 2009 amid post-election protests and a massive government crackdown. In March 2010, he was allowed a temporary release that was later extended, according to the website freekian09.org. The Iranian-American scholar is not allowed to leave the country, the website says.
• Journalist Roxana Saberi was arrested in January 2009 and convicted of espionage in a one-day trial that was closed to the public. She was freed in May that year.
• Literary translator Mohammad Soleimani Nia was detained in January 2012.
• Christian pastor Saeed Abedini was reportedly detained in September 2012.
CNN's Scott Bronstein and Drew Griffin contributed to this report