The city in China's restive Xinjiang region where a bomb attack killed 16 police was calm under sweeping security measures yesterday, three days before the Beijing Olympics.

Many residents of Kashgar declined to discuss Monday's incident, which China called a "suspected terrorist" attack carried out by two young men from the region's Muslim Uighur community who were detained on the spot.

Police stopped and checked all cars and buses entering the city, 5,000 kilometres west of Beijing, while riot police ringed the hospital where 16 officers injured in the attack were being treated and prevented reporters from talking to family members.

"We are scared that after this, things may be even harder for Uighurs," said a shopper in Kashgar's main market who gave only his first name, Ibrahim. "There's already a lot of tension here."

But an Uighur water seller said not everyone was worried and insisted the popular Silk Road tourist town was still safe.

"It is just because it is so close to the Olympics," he said. "But don't worry, this doesn't affect ordinary people like you and me," said the man, who declined to give his name.

In the latest step to tighten security before Friday's Olympics opening ceremony, the Xinjiang transport office announced a region-wide campaign to ensure the security of trucks, buses and transport hubs. "The whole region's transport network must establish a dense atmosphere of secure transport and production," the region's official news website (http://www.tianshannet.com) reported, citing an "urgent directive" from the government. Chinese state television reported that the two men who rammed a truck into a group of 70 policeman on a morning jog and then threw home-made bombs at them were a taxi driver and a vegetable seller from Kashgar.

Police found nine homemade explosives, a homemade gun and propaganda materials "promoting jihad", CCTV said. Police believed the "weapons were similar to those captured by police from an East Turkestan terror camp in January 2007", it added.

Xinjiang's largely Muslim Uighurs have been a focus of China's strict nationwide security in the run-up to the Games. Officials have said militants seeking an independent "East Turkestan" homeland are among the biggest threats.

Many Uighurs resent Chinese controls on religion and the expanding ethnic Han Chinese presence in Xinjiang, a region rich in energy and mineral resources.

The Global Times, a Chinese-language tabloid, quoted a Chinese anti-terrorism expert, Li Wei, as saying:

"We can't rule out that this was the work of a few East Turkestan supporters within the country who have links to external terrorist forces."

"East Turkestan terrorist forces are the most direct and most real terror threat to the Beijing Olympic Games," Mr Li added.

But Alim Seytoff, general secretary of the Uyghur American Association, a Washington DC-based group, said Monday's attack pointed more to discontent than militancy.

"We don't believe there are militant groups behind this," he said, adding that he had few details on the attack.

"But we do know the crackdown in Xinjiang, especially ahead of the Olympics, has increased discontent among Uighurs.

"The general mood is fear, official intimidation - a police-state fear," said Mr Seytoff.

China was taking no chances with the security of the August 8-24 games, the restive mountain region of Tibet held "anti-terror" exercises in recent days, the official Tibet Daily reported.

The exercises were held from August 2-4 around the railway station and airport of Lhasa, the regional capital, the report said. Lhasa was the epicentre of unrest in Tibet in March that spread across the vast mountain region.

Wang Bingyi, Tibet's top police and domestic security official, said the exercises were to "win a comprehensive victory in the security battle for the Olympics, and to protect the harmony and stability of Tibetan society".

China says followers of the exiled Dalai Lama pursuing independence for Tibet are engaged in terrorism, a claim dismissed by the Buddhist leader and many experts.

Factbox - Fortress Beijing: Security steps for the Olympics

Screening visitors:

• Visa rules have tightened. Travellers must now show a return air ticket and a hotel booking before buying a visa.

• Hong Kong, host of Olympic equestrian events and a major gateway to China, has created a watchlist of unwelcome activists, and brought in new visa restrictions ahead of the Games.

• Interpol is to give Beijing airport and other major border entry points access to its database of more than 14 million lost or stolen travel documents.

Security capabilities:

• A 100,000-strong security force, including the elite Snow Wolf Commando Unit, is already on alert for terrorists.

• 300,000 surveillance cameras watch the city.

• Since May, the team of People's Liberation Army (PLA) engineers is in charge of Games security checks and emergency rescues has run daily drills on finding and defusing explosives, rescuing and evacuating people from damaged buildings.

• The UN nuclear watchdog has trained Chinese security personnel to respond to radiological attacks - such as a "dirty bomb" - in which radioactive material is released.

Olympic venues:

• At least two surface-to-air missile launchers were set up in late June about a kilometre south of the Bird's Nest National Stadium.

• Authorities pledged to revamp public emergency shelters by the venues last October, saying 20 to 30 new shelters, with room for 1.5 million to two million people, were needed every year.

• Gas stations within 300 metres of Olympic venues and all Games-designated gas stations must install video surveillance equipment and "explosion-prevention devices".

• Unmanned spy planes will fly over the east coast city of Qingdao, host of sailing events, to scan for "suspicious activities".

Beijing City:

• Random identity card and passport checks have increased.

• Stringent security is in place on public transport with spot checks on bottled drinks, and x-ray machines and sniffer dogs deployed in subway stations to check commuters' luggage.

• Liquids, matches and lighters have been banned in hand luggage on domestic flights since officials said crew foiled an attempted airline bombing in Xinjiang in March.

• Fireworks have been banned from the Chinese capital for three months from July 1; and some bars and restaurants close to Olympics venues have been told to shut down.

• To prevent food safety problems or sabotage, inspectors will be posted in factories making food for the Olympics.

Restive regions:

• Chinese police said the bomb attack in Xinjiang's outpost city of Kashgar was a "suspected terrorist" attack. State television said yesterday the weapons used were similar to those seized in a police raid on an "East Turkestan terror camp" run by separatist Uighur militants in January 2007.