Christian persecution watchdog Voice of the Martyrs (VOM) has revealed that "foreign spies" and "native citizens working for a foreign intelligence service" in North Korea were in fact Christian believers.

At a press conference in Pyongyang in September, security service spokesman Li Su Gil said that the arrested persons "carried out the missions by means of diverse espionage equipment".

VOM said it had managed to identify the seven males and two female believers who were arrested.

VOM spokesperson, Tod Nettleton, said, "Following Jesus Christ is considered treason in North Korea, where the government mandates that worship is reserved for deceased dictator Kim Il Sung and his son, the current dictator, Kim Jong Il."

The Christians in question had started a portrait photography studio in order to support themselves and registered their business with the government authorities.

They were not involved in espionage work and the equipment taken by the government was for their portrait photography business, according to VOM.

"The Voice of the Martyrs is... deeply concerned for the well-being of our brothers and sisters there. We call on the North Korean Government to release these Christian believers, who were involved in legitimate business activities to support themselves and their families," said Nettleton.

"We pray that they are alive. But we know it is possible that they have finished their race on earth and gone on to their eternal reward in heaven.

"We encourage Christians everywhere to pray for our brothers and sisters in North Korea, who must constantly face the threat of arrest, torture and execution simply for living out their faith in Jesus Christ."

VOM has been engaged in aiding Christians in North Korea for decades. Among projects conducted by the persecution organisation in North Korea was the release of "Scripture balloons" which are mylar balloons filled with helium and printed with scripture passages on each side.