Pyongyang started building the network shortly after the Korean War
North Korea's capital Pyongyang has a network of secret tunnels which could be used as emergency escape routes by top officials, a defector has said.
The tunnels were built 300m (984 ft) below ground and stretch for some 50km (31 miles), Hwang Jang-yop told the Seoul-based Free North Korea Radio.
He claimed that one tunnel could be used by North Korean leader Kim Jong-il to escape to China.
Mr Hwang, a former secretary of North Korea's ruling party, defected in 1997.
Mr Hwang told the radio earlier this week that the secret underground network connected Pyongyang to several strategic sites across the hermit communist state.
One such tunnel linked Pyongyang to the port of Nampo, about 40km south-west of the city.
Mr Hwang also said that Mr Kim and his family members had an exclusive bunker linked by tunnels to Sunchon (about 40km north), which South Korea says has a uranium mine, and Yongwon (some 50km north-west), where his father, former leader Kim Il-sung, had a villa.
The defector claimed that the Sunchon tunnel had clean spring water and green grass.
He said North Korea had started building the underground network shortly after the armistice that halted the 1950-53 Korean war.
Pyongyang also has a 150-metre-deep underground railway, which could be used as a shelter for civilians in case of emergency.