TURPAN, China (REUTERS) - Chinese state media demanded severe punishment on Thursday after the government blamed militants from restive Xinjiang for an attack in Tiananmen Square, as the exiled leader of the region's Uighur minority called for an independent probe.

An SUV burst into flames on Monday after being driven into a crowd in Beijing's Tiananmen Square, the symbolic centre of China's power structure and one of the country's most closely guarded areas. The three occupants and two bystanders were killed, and dozens were injured.

Police said it was a "terrorist attack" carried out by people from Xinjiang, home to the Muslim Uighur people, and announced they had caught five accomplices who were planning holy war.

The ruling Communist Party's official People's Daily said the attack was a crime against humanity, adding that the government should spare no effort to ensure Beijing's safety.

"Violent terrorist crime is the shared enemy of all humanity, the shared enemy of all ethnic groups in the country, and it must be severely punished under the law," it said in an opinion piece on its website.

"Maintaining the capital's security and stability is a responsibility of utmost importance."

The English-language China Daily said the perpetrators will "go down in history as murderers not heroes".

Many Uighurs chaff at Chinese controls on their religion, culture and language, despite the government's protestations that they enjoy widespread freedoms. Xinjiang has been beset by violence, blamed by China on Uighur separatists and extremists.

But Ms Rebiya Kadeer, president of the Munich-based World Uighur Congress, the main exiled Uighur organisation, cautioned against believing China's account of the incident.

"Chinese claims simply cannot be accepted as facts without an independent and international investigation of what took place in Beijing on Monday," said US-based Kadeer, who lives in the Washington area.

China calls Ms Kadeer an "anti-Chinese splittist" and will almost certainly ignore her call for an international investigation. Authorities have said five suspected Islamist militants have been apprehended in connection with the incident - all of whom have names that suggest they are Uighur.

Authorities have moved to tighten security in energy-rich Xinjiang, and armed police prevented Reuters reporters from entering Lukqun, where one of the detained suspects is from, sending them back to the nearby city of Turpan.

Asked whether she believed Uighurs were responsible, Ms Kadeer said: "Maybe and maybe not. It is difficult to tell at the moment, given the strict control of information by the Chinese government on this tragic incident."

"If the Uighurs did it, I believe they did it out of desperation because there is no channel for the Uighur people to seek redress for any kind of injustice they had suffered under Chinese rule," she added.

Her comments were made in written replies to Reuters questions, translated from the Uighur language by an aide.

Ms Kadeer is a former Chinese political prisoner accused of leaking state secrets in 1999 who left China on medical parole and settled near Washington with her husband and part of her family in 2005. The 66-year-old mother of 11 previously had been a celebrated millionaire who had advised China's parliament.

Ms Kadeer said she feared the Tiananmen Square attack would join a long list of incidents that China uses "to justify its heavy-handed repression" in her native region.

She said she did not believe there was any kind of organised extremist Islamic movement operating in Xinjiang, a view shared by many rights groups and some experts.

"It is almost impossible for Uighurs to organise because of China's stringent controls and attacks."