WASHINGTON: The Iranian government has released four dual-national prisoners: Washington Post reporter Jason Rezaian, former US Marine Amir Hekmati, pastor Saeed Abedini and Nosratollah Khosravi-Roodsari, whose name had not been previously made public. A fifth American detained in Iran, Matthew Trevithick, was released in a move unrelated to the swap, US officials said. Matthew Trevithick, a student, was released after 40 days of detention at Evin Prison in Tehran, according to a statement from his parents. Trevithick had traveled to Iran in September for a four-month, intensive language programme at the Dehkhoda Institute, a language centre affiliated with Tehran University. He is co-founder of a research centre based in Turkey that assesses the humanitarian crisis in the area. Trevithick took a leave of absence from the centre in September to focus on increasing his fluency in Dari, a language closed related to Farsi. His parents said he learned the language while living in Afghanistan for four years. US officials said he was released earlier and was already on his way home, while the four in the negotiated swap were still in Iran on Sunday as work progressed to get them on a plane. Jason Rezaian, a reporter with The Washington Post, has been detained since July 2014 when Iranian security forces raided his home and seized his wife and him. Rezaian, who was born in California and holds both US and Iranian citizenship, was convicted in closed proceedings last year after being charged with espionage and related allegations. The length of his sentence has not been disclosed. The Post and the US government have denied the accusations, as has Rezaian. His wife, Yeganeh Salehi, was released on bail in October 2014. Rezaian was the Post's Tehran correspondent and was accredited to work in the country by the Iranian government. Rezaian, who has covered Iran for the Post since 2012, grew up in Marin County, California, and spent most of his life in the United States. The Post, US officials and Rezaian's family have all called for his release. Former US Marine Amir Hekmati of Flint, Michigan, was detained in August 2011 on espionage charges. His family says he has lost significant weight and has trouble breathing, raising fears he could contract tuberculosis. Hekmati says he went to Iran to visit family and spend time with his ailing grandmother. After his arrest, family members say they were told to keep the matter quiet. He was convicted of spying and sentenced to death in 2012. After a higher court ordered a retrial, he was sentenced in 2014 to 10 years on a lesser charge. His sister, Sarah, has said her brother renounces his dual Iranian citizenship and vows never to return to Iran if he's allowed to leave. He made the comments in a letter he dictated to his mother by phone. 'It has become very clear to me that those responsible view Iranian-Americans not as citizens or even human beings, but as bargaining chips and tools for propaganda,' he wrote in the letter sent to the State Department's Iranian interest section in Washington. 'Considering how little value the Ministry of Intelligence places on my Iranian citizenship and passport, I, too, place little value on them and inform you, effectively that I formally renounce my Iranian citizenship and passport.' Hekmati was born in Arizona and raised in Michigan. He and his family deny any wrongdoing, and say his imprisonment has included physical and mental torture and long periods of solitary confinement in a tiny cell. Pastor Saeed Abedini of Boise, Idaho, was detained for compromising national security, presumably because of Christian proselytising, in September 2012. He was sentenced in 2013 to eight years in prison. US President Barack Obama met his wife and children in 2015. There are claims he was beaten in Iranian prison. Abedini was previously arrested in 2009 and released after promising to stop organising churches in homes. At the time of his arrest, he was running an orphanage in Iran. The fourth is Nosratollah Khosravi-Roodsari, whose name had not been previously made public.