IntelCenter, a US-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.

"The Turkistan Islamic Party volunteers who had gone through special preparations have started urgent actions."

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 plastic factory in Guangzhou on July 17 and bombed three public buses in Yunnan on July 21, according to IntelCenter.

The bus explosions killed at least two people and injured 14 in the south-western city of Kunming on Monday amid a security clampdown ahead of the Olympics.

The official Xinhua news agency had blamed the blasts on "sabotage" and was seeking to find out who was responsible.

"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 mind.