BEIJING, July 26 (Reuters) - Chinese authorities denied claims by a group calling itself the Turkistan Islamic Party that it was responsible for deadly bus explosions in Shanghai and Yunnan province ahead of the Olympic Games, the official Xinhua news agency reported on Saturday.

The group released a video threatening the Beijing Olympic Games and claiming responsibility for deadly bus explosions in Shanghai and in Yunnan's Kunming, a terrorism monitoring firm in Washington said on Friday.

But Xinhua reported that a police investigation of the Shanghai blast on May 5 had nothing to do with "terrorist attacks".

The blast, which killed three people and wounded 12, was caused by inflammables such as oil, Cheng Jiulong, Shanghai Municipal Public Security Bureau deputy head, was quoted by Xinhua as saying.

"The blast was indeed deliberate but had nothing to do with terrorist attacks," he said.

IntelCenter, a U.S.-based terrorism monitoring firm, said the group had released a video entitled "Our Blessed Jihad in Yunnan", featuring a statement by the group's leader, Commander Seyfullah, threatening next month's Olympics.

"Despite the Turkistan 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 Seyfullah as saying.

Seyfullah said the group bombed two public buses in Shanghai on May 5 and "took action against police" in Wenzhou on July 17 with a tractor loaded with explosives.

The group also bombed a plastics factory in Guangzhou on July 17 and bombed three public buses in Yunnan on July 21, according to IntelCenter.

The Xinhua report did not specifically address the group's other claims.

Bus explosions killed at least two people and wounded 14 in the southwestern city of Kunming on Monday.

"The Turkistan Islamic Party warns China one more time," Seyfullah said, according to the IntelCenter transcript.

"Our aim is to target the most critical points related to the Olympics. We will try to attack Chinese central cities severely using the tactics that have never been employed."

He urged spectators and athletes "particularly the Muslims" planning to attend the Olympics to change their minds.

The warning comes two weeks before the start of the Beijing Games on Aug. 8. (Reporting by Ken Wills in Beijing and Deborah Charles in Washington; Editing by David Fogarty)

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