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 - blamed on separatist Muslim militants - that killed 16 policemen in the western region of Xinjiang.
A spokesman for the organisers said preparations had been made to meet all conceivable threats at Games' venues.
Meanwhile, Japan is probing reports police hit two journalists in Xinjiang.
The journalists, a reporter and a photographer, said they were detained for two hours near the site of Monday's attack in Kashgar.
Police pushed them to the floor and punched them, they said.
Japan's top government spokesman, Nobutaka Machimura, said diplomats were looking in to it.
"Our embassy is of course gathering information from the authorities," Reuters quoted him as saying. "I believe there is no mistake, so we plan to protest strongly."
'Prepared to respond'
China is working to play down any threat to the Games in the wake of Monday's 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".
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 in Kashgar, the agency said.
Kashgar, known as Kashi in Chinese, is some 4,000km (2,500 miles) from Beijing, near the border with Tajikistan.
Early on Monday, two men drove a rubbish truck into a group of policemen, then attacked them with grenades and knives. The two men were later arrested, Xinhua news agency said.
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 is making organisers nervous, says the BBC's James Reynolds in Xinjiang.
But, says our reporter, at the scene itself there is almost no trace of the incident, apart from three uprooted trees.
Uighur suppression
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.
Last week, a senior Chinese army officer warned that Islamic separatists were the biggest danger to the Olympics.
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."
(Source: BBC)
