North Korea's Supreme Court has convicted two South Koreans on state subversion charges and sentenced them to life in prison with hard labour.

The sentences for Kim Kuk-gi and Choe Chun-gil were handed down Tuesday after they were found guilty of spying for South Korea's National Intelligence Service (NIS) from the Chinese border city of Dandong.

Officials in South Korea have denied they were involved in espionage and demanded they be released.

North Korea presented the two before reporters in March and said they had been taken into custody last year.

Under North Korean law, the sentences are final and cannot be appealed.

The pair were charged with conspiracy to overturn the state, espionage, and illegal entry and were accused of working under the control of the US and South Korean governments, South Korean news agency Yonhap reported, citing North Korean state radio.

Seoul's Unification Ministry, which handles ties with the North, could not immediately confirm the North's broadcast.

North and South Korea are still technically at war after their 1950-53 conflict ended in a truce, not a treaty.

The reclusive North, which regularly threatens to destroy the United States in a sea of flames, has also been slapped with heavy Western sanctions over its nuclear and missile programmes.

Source: Agencies