Beijing police arrested five suspects and accused them of planning the fiery crash Monday.
In a statement issued in Washington after the crash, Rebiya Kadeer, president of the World Uighur Congress, which represents the Uighurs in China's ethnically tense Xinjiang-Uighur province, said the Chinese government will not hesitate to "concoct a version of the incident in Beijing" to further impose repressive measures on its people.
The Turkic-speaking Uighurs, who call the Xinjiang region "East Turkestan" and seek autonomy, resent being ruled by Han Chinese. They have staged a number of demonstrations to press demands and dozens of Uighurs have died in a Chinese crackdown on the protests.
Chinese censors clamped down on the reporting of the vehicle crash immediately after it occurred and held off answering questions on whether it was terror-related or a suicide attempt. There have been a number of self-immolations by Tibetans who also have protested Chinese rule of Tibet.
The crash killed five people and 40 others were injured. Those killed included two people on the square besides the driver and two other occupants after the vehicle caught fire.
Tiananmen Square is known for the 1989 pro-democracy student protests crushed by the military.
Terrorist attacks carried out by extremists from the Xinjiang-Uighur region have spread outside the region and become more difficult to prevent, the official China Daily reported Thursday, quoting experts.
"The attack was carefully planned, organized and premeditated," a spokesman for the Beijing Public Security Bureau said Wednesday.
Police said the driver, identified as Usmen Hasan, accompanied by his mother Kuwanhan Reyim and wife Gulkiz Gini, drove a jeep with a Xinjiang license plate into a crowd of people.
Police said the three in the jeep died after gasoline stored in containers inside the vehicle caught fire. The official Xinhua News agency said police found gasoline, two knives and steel rods as well as a flag with extremist religious content in the jeep.
"It is an obvious suicide attack," Ma Pinyan, an anti-terrorism researcher at the Xinjiang Academy of Social Sciences in the provincial capital of Urumqi, told China Daily. He said the incident showed "the whole family was under the strong influence of extremist religion, which has led to an increasing number of attacks in Xinjiang in recent years."
Ma said in targeting the Tiananmen Square in the heart of China's capital, the attackers "want to generate a greater sense of fear and international impact."
Li Wei at the China Institutes of Contemporary International Relations said Monday's attack was similar to the July 30, 2011, attack in Kashgar when terrorists drove a vehicle into a crowd, killing eight people, China Daily said.
"Effectively curbing the spread of extreme religion in Xinjiang, which is the source of the problem, remains a challenge for authorities in the region as well as the central government," Ma said.
Xinhua reported police also found knives and at least one "jihad" flag in a temporary residence of the detained suspects, who admitted they knew the driver and conspired to plan the attack.
The Washington Post said the arrest of the five could further heighten tensions between the Uighurs and the Chinese government, leading to tighter police controls in Xinjiang. The suspects were identified by police as Husanjan Wuxur, Gulnar Tuhtiniyaz, Yusup Umarniyaz, Bujanat Abdukadir and Yusup Ahmat.
A spokesman for the Uighur group told the Post police had arrested 93 Uighurs, not just the five announced.