China has defended its detention of an American-based academic who was carrying out research into the ill-fated Cultural Revolution - in which millions were persecuted by Chairman Mao and his wife in the late 1960s and early 1970s.

Scholars from around the world have called for the release of Song Yongyi - a Chinese national who works as a university librarian in Pennsylvania - saying his prosecution would make it impossible to conduct open research in China.

Mr Song - who spent five years in jail during the Cultural Revolution - was detained in August while on a trip to China to study newspaper archives. The Chinese authorities say he's suspected of breaking China's criminal code and illegally obtaining intelligence. Mr Song's wife said all the material he'd collected was from newspapers and other open sources.

The BBC Beijing correspondent says the Chinese authorities have accepted that the Cultural Revolution was a great disaster.

But he says they've still not permitted a full and open debate about its causes and implications.

From the newsroom of the BBC World Service