Police have denied a Uygur separatist group's claim of masterminding the recent bus explosions in Shanghai and Kunming, and said they had nothing to do with attempts to disrupt the Olympic Games.

A group known as the Turkistan Islamic Party has released a video clip, threatening to disrupt the August Beijing Olympics, said AFP and Reuters.

The news agencies cited reports issued by IntelCenter, a Washington-based terrorism-monitoring organization.

Though the Ministry of Public Security has declined to comment on those responsible for the blasts, police officials in Shanghai municipality and Yunnan province denied the Turkistan Islamic Party's claim.

On Saturday, Shanghai police reiterated that the May 5 bus blast in the Olympic co-host city had nothing to do with "terrorism."

"The blast was deliberate but it had nothing to do with terrorism," said Cheng Jiulong, deputy head of the Shanghai municipal public security bureau.

An investigation shows inflammable substances caused the blast, in which three persons were killed and 12 injured.

Chen said on Wednesday that Shanghai police foiled a terrorist group's bid to attack a preliminary venue for the Olympics soccer games.

"We have information that international terrorist organizations could attack an Olympic venue in the city and we have busted a group of terrorists," he said.

But he did not give details on when, where or how many terrorists were nabbed.

In Kunming, capital of Yunnan province, two explosions ripped through two buses in the space of an hour on the morning of July 21, leaving two dead and 14 injured.

But "so far no evidence has been found to indicate the explosions were connected with terrorists or with the Beijing Olympics", said a spokesman for the Yunnan provincial public security bureau on Saturday.

It is, however, not yet clear whether the explosions were carried out by a group or just an individual, he said. "Investigation is ongoing."