A top Chinese economist was barred from leaving the country last week for national security reasons, as Beijing tightens its grip on academics and other dissenting viewpoints.

Sheng Hong, executive director of the independent Unirule Institute of Economics, told dpa yesterday that he was barred from travelling to Boston last week, where he was to attend a conference at Harvard University. Sheng made it as far as the airport on Thursday when he was stopped by the Beijing Public Security Bureau, which was acting, he believed, on the orders of the State Council.

"This should not have happened," he told dpa. "They said that it was harmful to national security. This is without any [legal] basis." The decision to block Sheng's trip may have been linked to a critical article published on the Financial Times' Chinese website last week.

In the piece, Sheng said China was in danger of abandoning the landmark reforms of Deng Xiaoping, who opened the country's economy in 1978 following the death of Mao Zedong.