A 21-year-old Iranian has been sentenced to death for 'insulting Islam' on an instant messaging app.

Sina Dehghan was arrested in October 2015 in Tehran after he caused offence on a messaging service called LINE.

But after his arrest activists claim he was duped into signing a confession after being told if he claim clean he would be released.

But instead his death penalty was confirmed in January when it was upheld by the Supreme Court, according to the Center for Human Rights in Iran (CHRI).

'During his interrogation, Sina was told that if he signed a confession and repented, he would be pardoned and let go,' a source told CHRI. 'Unfortunately, he made a childish decision and accepted the charges. Then they sentenced him to death.'

'Later he admitted that he signed the confession hoping to get freed,' added the source. 'Apparently the authorities also got him to confess in front of a camera as well.'

The human rights group have launched a judicial review against the death sentence which is currently being processed.

Dehghan was a conscript posted to a military barracks in Tehran when he was arrested, four days before he was due to leave the army.

'They took him to his home and searched it while he repeatedly expressed regret and repentance,' a source told CHRI.

According to Iran's Islamic Penal Code, insulting the prophet is punishable by death. But Article 263 says that if the accused tells the court that the insults were a result of anger or a mistake, the sentence can be reduced to 74 lashings.