Days before the Olympic Games open in Beijing, the Chinese authorities have said they are confident that athletes and spectators will be safe.
This assurance comes after an attack which killed 16 policemen in the western region of Xinjiang.
A spokesman for the Beijing Games Organising Committee said preparations had been made to meet every conceivable threat at Games' venues.
Chinese media have blamed separatist Muslim militants for the attack.
"China has focused on strengthening security and protection around Olympic venues and at the Olympics Village, so Beijing is already prepared to respond to any threat," Beijing Games spokesman Sun Weide was quoted as saying.
The International Olympic Committee said it also believed the Chinese authorities had done everything possible "to ensure the security and safety of everyone at the Games".
In Monday's attack two men reportedly drove up to a border post in a rubbish truck and threw two grenades, before moving in to attack the policemen with knives.
Both attackers were captured during the raid near the city of Kashgar, Xinhua state news agency reported.
Kashgar, known as Kashi in Chinese, is some 4,000km (2,500 miles) from Beijing, near the border with Tajikistan.
Although the episode happened a long way away from Beijing, the very fact that it happened four days before the opening ceremony of the Olympic Games, will make the organisers nervous, says the BBC's James Reynolds in Xinjiang.
About 100,000 police and soldiers are on standby ahead of Friday's opening ceremony, and the already tight security has been stepped up in Tiananmen Square.
Security has also been beefed up in Xinjiang, Xinhua news agency said. Police intensified road checks and increased personnel at government offices, schools and hospitals, the agency said.
Meanwhile Japan says it plans to protest after two journalists covering the attack said they were detained and beaten by police.
The journalists, one from a regional daily the Chunichi Shinbun and the other from Nippon television, said they were held for two hours in Kashgar and struck by police.
"Our embassy is of course gathering information from the authorities," Reuters quoted Japan's top government spokesman, Nobutaka Machimura, as saying.
"I believe there is no mistake, so we plan to protest strongly."
Xinjiang, in the north-west of the country, is home to the Muslim Uighur people. Uighur separatists have waged a low-level campaign against Chinese rule for decades.
Human rights groups say Beijing is suppressing the rights of Uighurs.
Col Tian Yixiang of the Olympics security command centre told reporters the main threat came from the "East Turkestan terrorist organisation".
The term is used by the government to refer to Islamist separatists in Xinjiang.
Late last month a group called the Turkestan Islamic Party said it had blown up buses in Shanghai and Yunnan, killing five people.
But China denied that the explosions were acts of terrorism.
The Washington-based IntelCenter, which monitors terrorism communications, said the Turkestan Islamic Party had released a video entitled Our Blessed Jihad in Yunnan.
In it, the group's leader, Commander Seyfullah, said it was responsible for several attacks and threatened the Olympics.
"The Chinese have haughtily ignored our warnings," IntelCenter quoted him as saying.
"The Turkestan Islamic Party volunteers... have started urgent actions."