China has defended the detention of a US-based academic who was carrying out research into the Cultural Revolution.

A group of 101 academics on Wednesday sent a petition to China's President Jiang Zemin calling for the release of Song Yongyi, a Chinese national who works as a university librarian in Pennsylvania.

They said he was simply collecting newspapers from the Cultural Revolution period when he was detained last August.

But China's Foreign Ministry spokesman said Mr Song was suspected of breaking China's criminal code and illegally supplying intelligence.

Mr Song's wife was detained with him and released after three months, but he is reported to have been formally arrested in late December.

Mr Song, a librarian at Dickinson College who holds US permanent residence rights, is a leading expert on China's Cultural Revolution of the late 1960s and early 1970s and author of a number of books and papers.

Book club revolutionary

The petition from scholars in the US, Canada and Hong Kong, said prosecution of the case against him would make it impossible for academics to conduct open research in China.

But China's Foreign Ministry spokesman, Zhu Bangzao, said Mr Song was under suspicion of illegally buying and passing on intelligence with financial backing from outside China.

He said investigations were being conducted according to Chinese law and people should not make what he called irresponsible remarks about the case.

Mr Song's wife, Helen Yao, has said that all the material collected by her husband was from newspapers and other open sources.

Song Yongyi himself spent five years in jail during the Cultural Revolution, labelled a counter-revolutionary for joining a book club.

The Chinese authorities have accepted that the Cultural Revolution, in which millions were persecuted, was a great disaster, but they have still not permitted a full and open debate about its causes and implications.