While North Korea continues to bar missionaries from entering the country, the Gospel is instead being carried across the border through the airwaves.

Christian evangelist Dr Billy Kim told BBC World that radio is the 'next best thing' to spread the Gospel so long as the communist country remains closed off to missionaries and other outsiders.

He is chairman of FEBC, a radio ministry that broadcasts Christian programmes from Seoul in South Korea.

'They don't allow us to come in - any missionaries or preachers,' he said. 

'So the next best thing would be the AM radio wave to send the Gospel to North Korea.' 

In addition to airing Christian radio programmes that can be picked up in the North, radios are smuggled across the border with China. 

There are severe penalties for North Koreans caught practising the Christian faith, including execution, torture or imprisonment in hard labour camps. 

Dr Kim told BBC World that for Christians listening to FEBC's programmes from North Korea, the radio station 'is their church'. 

He said that some people who had escaped the isolated country told him that 'under the blanket they are listening'. 

FEBC radio presenter and North Korean defector Ju Chan-yang told BBC World she used to listen to the Christian radio shows when she was still inside North Korea and that she hopes her old friends are listening.

'They just say personal love and cares and free and human rights.  That was very - yes, that was our hope and dream,' she said. 

North Korea is ranked number one on Open Doors' World Watch List of the 50 countries where Christians suffer the most for their faith. It has topped the World Watch List for the last 18 years in a row. 

Open Doors said that renewed diplomatic efforts between North and South Korea have not lessened the persecution against Christians. 

'In fact, reports indicate that local authorities are increasing incentives for anyone who exposes a Christian in their community,' it said earlier this month.

'If Christians are discovered, not only are they deported to labor camps or even killed on the spot, their families to the fourth generation share their fate as well.

'Communal worship is non-existent. Daring to meet other Christians for worship is a risky feat that must be done in utmost secrecy.

'Yet Open Doors estimates the number of Christians in North Korea to be 300,000 strong—believers who are defying the unjust regime and following Jesus.'