China's Communist Party has expelled the military commander of Xinjiang from its ranks, state media reported Sunday, after an attack in Beijing officially blamed on members of the Uighur minority in the troubled northwest region.

General Peng Yong, who was named commander of the Xinjiang military region in July 2011, was dismissed from his post as a member of the Standing Committee of the Chinese Communist Party of Xinjiang, the Xinjiang Daily said in a terse dispatch.

The state-run paper did not give a reason for Peng's removal but it comes after last Monday's attack in Tiananmen Square, which was a major embarrassment for the enormous state security apparatus.

Xinjiang has been the scene of several violent clashes, the most recent of which left dozens dead in April, June and August this year.

After being stripped of his party post, Peng is likely to be relieved of his military responsibilities in the far-west region where China's mostly Muslim Uighur minority is concentrated.

According to Chinese police, three Xinjiang Uighurs drove their car loaded with petrol canisters into the gate of the Forbidden City in an attack that left two dead, besides the three people in the car, and 40 injured.

Chinese state television said the attack was carried out by a group of eight "terrorists" who possessed weapons including "Tibetan knives and 400 litres of petrol".

China's top security official Meng Jianzhu has accused the separatist East Turkestan Islamic Movement of supporting the attack.

The authorities have, however, not provided any evidence to support this assertion, which has raised doubts among experts given the amateurish nature of the attack and the lack of an established Islamic extremist foothold in China.

Also according to police, the three occupants of the car were members of the same family: driver Usmen Hasan was accompanied by his mother and his wife.

In a statement sent to AFP Sunday, Radio Free Asia (RFA) said the man could have been acting out of personal revenge over a double tragedy.

Citing two anonymous Uighur sources, RFA said Hasan, 33, had lost a family member during the 2009 ethnic riots in the Xinjiang capital Urumqi.

His younger brother had also died in a mysterious car accident which had been blamed on the majority Han Chinese or the authorities.

AFP was unable to confirm these allegations but RFA, which is funded by the US Congress, has good contacts within the Uighur population of Xinjiang.

Separately, the head of the Communist Party in Beijing, Guo Jinlong, said it must "learn" from the attack and identify "weak links", according to an article published Sunday by the Beijing Daily, the official mouthpiece of the party in the capital.

"Draconian prevention of violent terrorist attacks is part of the mission in maintaining order", he said.

Xinjiang has been sporadically rocked by unrest that authorities have usually blamed on "terrorists" and "separatists".

But Uighur organisations dismiss claims of terrorism and separatism as an excuse by Beijing to justify religious and security restrictions.

Beijing says its policies and investment in Xinjiang have brought tremendous development. But critics counter that the economic growth mostly benefits an influx of ethnic majority Han Chinese, millions of whom have moved to the resource-rich region.

Ethnic frictions have risen in Xinjiang as a result, and rioting in Urumqi involving both ethnic groups in 2009 left 200 people dead.