Chinese authorities have dismissed claims by a militant Islamist group that it was responsible for recent explosions on buses.
The Turkestan Islamic Party said that it had blown up buses in Shanghai and Yunnan, killing five people.
It also said that it was planning attacks on the Olympic Games.
Although China denies the explosions were acts of terrorism, it has recently arrested alleged militants it says were planning attacks on the games.
Critics say China has been exaggerating such threats to justify repressive measures in the mainly Muslim Uighur region of Xinjiang in the north-west.
In Yunnan province, two explosions on buses last Monday left two people dead.
But a public security official in Yunnan, quoted by the official Xinhua news agency on Saturday, said no evidence had been found linking the explosions with terrorism.
In Shanghai, where three people died in an explosion in May, police also denied a link to terrorism, Xinhua said.
The Washington-based IntelCenter, which monitors terrorism communications, said the Turkestan Islamic Party had released a video entitled Our Blessed Jihad in Yunnan.
Ethnically Turkic Muslims, mainly in Xinjiang
Made bid for independent state in 1940s
Sporadic violence in Xinjiang since 1991
Uighurs worried about Chinese immigration and erosion of traditional culture
In it, the group's leader, Commander Seyfullah, said it was responsible for several attacks and threatened next month's Olympics.
"Despite the Turkestan Islamic Party's repeated warnings to China and international community about stopping the 29th Olympics in Beijing, the Chinese have haughtily ignored our warnings," IntelCenter quoted him as saying.
"The Turkestan Islamic Party volunteers who had gone through special preparations have started urgent actions."
Earlier this month, Chinese officials said they had broken up five terrorist groups in the Xinjiang region which had been planning attacks on the Olympic Games.