An Iranian convert to Christianity has had his 10-year prison sentence for 'missionary activities' upheld after losing his appeal, World Watch Monitor has reported.

Naser Navard Gol-Tapeh was sentenced in May alongside three Azerbaijanis, and all four men were given 10-year sentences for 'missionary activities' and 'actions against national security' in Iran.

However, the three Azerbaijanis – Eldar Gurbanov, Yusif Farhadov and Bahram Nasibov – were released from Iran in November 2016 and, according to WWM, are unlikely to be forced to return, despite their representatives also failing to overturn their verdicts during the hearing on November 12.

The four men were arrested after security agents raided a wedding party in Tehran in June 2016, according to WWM. They spent four months in prison before being released on bail, after which the Azerbaijani men travelled home.

The charges were described as 'unwarranted and unjustifiable' by Mervyn Thomas, the chief executive of Christian Solidarity Worldwide (CSW).

According to the advocacy group Article 18, 21 Christians have been sentenced to long prison terms in Iran since May.

Iran is ranked 8th on the Open Doors 2017 World Watch List of the 50 countries in which it is most difficult to live as a Christian.

In 2016, over 193 Christians were arrested for attending these prayer meetings and Bible studies in 'house churches' according to WWM.