Chinese police have increased security in the country's north-western Xinjiang province amid claims that thousands of Falun Gong followers have been rounded up elsewhere in the country in the run-up to the Olympic Games.

The Xinjiang crackdown came in response to an attack which killed 16 policemen on Monday.

Chinese police are now checking all cars and buses entering the city of Kashgar, while riot police have ringed the hospital where injured officers are being treated.

Authorities say two local ethnic Uighur men, a taxi driver and vegetable-seller, were responsible for killing 16 officers and injuring 16 more.

State television said police found propaganda materials promoting jihad and weapons similar to those captured from a terrorist camp last year.

The exiled World Uighur Congress says many people have been rounded up in the wake of the attack, and some have been beaten.

Local authorities have also announced the arrest of 18 foreign agitators, but say they were not involved in Monday's attack.

Falun Gong arrests claim

The director of the Association for Asian Research, Erping Zhang, also says the Chinese Government has rounded up thousands of Falun Gong practitioners.

Mr Zhang says the Government has used the Games to crack down on dissenting voices, including members of underground churches and pro-democracy intellectuals and activists.

He told ABC TV's Lateline that the Chinese Government has detained 8,000 members of the banned spiritual movement Falun Gong.

"There are reports from different sources, from rights groups that they were rounded up in the run-up to the Games and they have been sent to a place nobody knows," he said.

"Even the family members cannot identify the location."