BEIJING Suspected Muslim separatists with homemade bombs killed 16 police in western China on Monday, state media said, reporting one of the worst attacks by militants on Chinese soil just four days before the Olympics.
The attack, about 4,000 km (2,500 miles) from the capital in the old Silk Road city of Kashgar, was a reminder of internal tensions in China, especially in its largely Muslim west.
Police had warned ethnic Uighur separatists were planning attacks in the run-up to the Games. They said they arrested the two attackers in Kashgar and identified them as Uighurs.
China's President Hu Jintao told a meeting of the International Olympic Committee (IOC) the Games would display the desire of the world's most populous country to join with the rest of the planet in "building a bright future".
The Beijing Organizing Committee of the Games said it was sure athletes and spectators would be safe, while the IOC also reassured millions of visitors and more than 10,000 athletes taking part in what it called a "landmark event".
"The IOC is confident the Chinese authorities have done everything possible to ensure the security and safety of everyone at the Games," it said in a statement.
About 100,000 police and soldiers are on standby ahead of Friday's opening ceremony, and security has been stepped up in Tiananmen Square, scene of the 1989 pro-democracy uprising, with all visitors' bags being screened.
American swimming phenomenon Michael Phelps slipped into town to begin an Olympic adventure that could end with him breaking Mark Spitz's record of seven golds in one Olympics.
The lanky 23-year-old eluded female fans and a media scrum in the arrivals hall at Beijing's vast new international airport terminal, entering the country through a side door.
Phelps won six gold and two bronze medals at the 2004 Athens Olympics and will get a $1 million bonus from sponsor Speedo if he can equal compatriot Spitz's haul from the 1972 Munich Games.
There is a strong sense of excitement in the city, but the number of foreign visitors has been disappointing. Hotels said they were slashing room prices by as much as half because reservations have fallen far short of expectations.
TICKET SCAM
People are thought to have shied away because of visa restrictions and bad publicity about China. Thousands more fans had their hopes of coming dashed after being swindled by an international Internet scam offering bogus tickets.
The IOC said it was taking action to shut down the fraudsters, but it was too late to help victims from the United States, China, Australia, New Zealand, Japan, Norway and Britain, including relatives of some athletes.
The IOC said it filed a lawsuit in California against six Web sites last Friday, but a U.S. lawyer who said he had lost $12,000 in the scam accused Olympic officials of complacency.
"They have known about these sites for months and months and did nothing," said Jim Moriarty, partner of a Houston-based firm which is looking to represent fellow victims.
Beijing's pollution-fuelled haze was back on Monday after three rare blue-sky days, but authorities said air quality was fairly good. The Communist government says drastic measures -- like ordering nearly 2 million of the city's cars off the road and closing smoke-belching factories -- have helped.
The Games organizers blamed the smog on a lack of wind. "We hope it is fine on Friday," said spokesman Sun Weide. "That depends not only on human endeavor but on Mother Nature too."
China's leaders hope the Games will showcase their country's economic progress and new global clout.
The Olympic torch took a ceremonial lap through a stadium on the edge of China's quake-hit Sichuan province on Monday, with children from affected areas brought in by bus. The quake killed 70,000 people in May.
"The Olympics give the survivors here a bit of encouragement," said 22-year-old Zhao Mulan, cradling her four-month-old son. "It gives us confidence that China is very strong and that our lives will be better and better."
But the Games have also galvanized critics of China on a range of issues from treatment of internal dissidents, particularly in Tibet, censorship of the Internet, and Beijing's close ties with Sudan's government despite the Darfur conflict.
A small group of people, shouting and waving their fists, demonstrated close to Tiananmen Square. The official Xinhua news agency said they wanted better compensation after their houses were demolished to make way for pre-Olympic redevelopment.
SEPARATISM
In Kashgar in the remote Xinjiang region, attackers drove up and tossed home-made bombs at police jogging through the street on their morning exercises on Monday, Xinhua reported. In addition to the 16 police killed, 16 officers were wounded.
Kashgar was calm late on Monday evening, with a heavy security presence around the scene. A crowd gathered and was dispersed forcefully by security men with batons.
"Ahead of the Olympics, it is a very powerful symbolic attack because security in Xinjiang is at an all-time high," said Nicholas Bequelin of Human Rights Watch.
Xinjiang is home to some 8 million Muslim, Turkic-speaking Uighurs. Many harbor resentments similar to those of Tibetans -- against Chinese controls on religion and the big influx of majority Han Chinese migrants into their region.
Authorities have named the Xinjiang separatist "East Turkistan Islamic Movement" as a threat to the Olympics.
But in Beijing, public excitement over the Games mounted. Several hundred thousand smiling volunteers, mainly students, man every street corner to shepherd visitors around.
"You see, we are not as nasty as some of you in the Western media say we are," said one 21-year-old female engineering student, handing coffee to visiting reporters.
(Additional reporting by Crispian Balmer, Alan Baldwin, Simon Rabinovitch, Emma Graham-Harrison, Nick Mulvenney and Guo Shipeng; writing by Simon Denyer; editing by Andrew Roche)
(For more stories visit our multimedia website "Road to Beijing" here)
Sixteen policemen were killed by unidentified assailants in , in the predominantly Muslim  region of China. Another sixteen officers were wounded in the attack, in which two attackers drove a lorry into the station. The government of the People's Republic of China has repeatedly warned of unrest leading up to the 2008 Summer Olympics.

Xinhua News Agency reports that the attackers drove a dump truck into the police officers during the officers' morning exercise at about 8:00 am local time (0:00 GMT), then threw grenades into the police barracks and attacked with knives. The BBC reports that fourteen of the police deaths occurred at the scene, with two more dying en route to hospital. They also report one of the alleged attackers received a leg injury. The attackers were arrested, according to police.

After they were arrested by the police, the assailants were described as being 28 and 33, and of the  minority, a  speaking people who reside primarily in the Xinjiang region. The police found an additional 10 explosives in the truck as well as what was described as  a "home-made gun." 

The autonomous Xinjiang region of China is a large, sparsely-populated territory in the north-west of the country. The population includes many groups, but the largest is the  including the largely Muslim . Kashgar is an oasis city at an important junction of trade routes, near China's western borders, and was a part of the historic "."