The two countries have been spying on each other since splitting after a civil war in 1949.
China claims self-ruled, democratic Taiwan as part of its territory to be seized one day, by force if necessary.
The two sides have been spying on each other since splitting after a civil war between Chinese nationalists and communists in 1949. Liu received a combined sentence of 20 years for his offences, which the court did not provide details on as the case concerns national secrets, it said in a statement.
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