(AFP) - A US freedom-of-religion monitor has welcomed the release of an Iranian Christian who had worked with a once-imprisoned Iranian-American pastor freed in a January 2016 prisoner swap.

Maryam Naghash Zargaran, a Christian convert from Islam, was sentenced in 2013 to four years in prison on charges of acts against national security.

The US Commission on International Religious Freedom, a government watchdog, said Zargaran was imprisoned apparently in connection with her work at an orphanage alongside Iranian-American Christian pastor Saeed Abedini.

Zargaran, 39, was arrested soon after Abedini was detained.

She "suffered unjustly in prison for more than four years simply due to her Christian faith," said USCIRF Commissioner Clifford May in a statement Thursday.

Zargaran was released from Evin prison in Tehran on August 1 "and was welcomed by friends and family," according to the Human Rights Activists news agency (HRANA), a US-based human rights organization monitoring events in Iran.

According to the HRANA, Zargaran went on hunger strike several times to protest her sentence and lack of medical care for her heart problems.

Abedini was released in January 2016 as part of a prisoner exchange that included The Washington Post's Tehran correspondent Jason Rezaian, who had been detained in Iran for nearly 18 months, and former US Marine Amir Hekmati, all of whom have dual US-Iranian citizenship.