Wang Lequan, the top Communist Party official in the far western region of Xinjiang, said materials seized in a Jan. 27 raid in the regional capital, Urumqi, showed the plotters' planned "specifically to sabotage the staging of the Beijing Olympics."
"Their goal was very clear," Wang told reporters at a meeting of Xinjiang delegates in Beijing.
Wang cited no other evidence or sources of the information and earlier reports on the raid had made no mention of Olympic targets.
Speaking at the same meeting, Xinjiang's governor said a flight crew prevented an apparent attempt to crash a China Southern flight from Urumqi to Beijing on Friday. Nur Bekri did not specifically label the incident a terrorist act, saying it remained under investigation. No passengers were injured and police were investigating, he said.
The incidents may give greater force to China's arguments that extreme measures are necessary to ensure social stability and the safety of August's Olympics.
While deadly violence is less common in China than in many countries - Beijing bans virtually all private gun ownership - officials were quick to assert that a hostage drama involving 10 Australian travel agents last week was not an embarrassment in the run-up to the Olympics.
The hostage-taker was shot and killed by a police sniper after an almost three-hour standoff in the northern tourist hub, Xi'an. The motive was not known.
Chinese forces have for years been battling a low-intensity separatist movement among Xinjiang's Uighurs, a Turkic Muslim people who are culturally and ethnically distinct from China's Han majority. China has largely suppressed the violence, however, and no major bombing or shooting incidents have been reported in almost a decade.
China has ratcheted up anti-terror preparations ahead of the Games, with the nation's top police official last year labeling terrorism as the biggest threat facing the event.
Terrorism experts say the threat is low given China's tight social controls, but warn that Beijing's counterterrorism capabilities are weak, especially in intelligence gathering and analysis.
Earlier reports of the Janary raid in Urumqi said police found guns, homemade bombs, training materials and "extremist religious ideological materials". Two members of the gang were killed in the raid and 15 arrested. Authorities have not identified those killed and arrested or their targets.
The Global Times newspaper published by the Communist Party had earlier said the group planned bombings and other "violent terrorist incidents" for Feb. 5, the last business day before the start of the Lunar New Year holiday.
Wang said the group was been trained by and following the orders of a Uighur separatist group based in Pakistan and Afghanistan called the East Turkestan Islamic Movement, or ETIM. The group has been labeled a terrorist organization by the United Nations and the United States. East Turkestan is another name for Xinjiang.
China says its main terror threat comes from ETIM. Although the group is believed to have no more than a few dozen members, terrorism experts say it has become influential among extremist groups using the Internet to raise funds and find recruits.
Chinese forces reported raiding an ETIM training camp last year and killing 18 militants allegedly linked to al Qaeda and the Taliban.
"These guys are fantasizing if they think they can disrupt the Olympics," said Wang, known for his hardline stance on crushing dissent. "They don't have the strength."
Few details were available about the alleged attempt to crash the China Southern Airlines flight Friday morning. Bekri indicated that more than one person was involved, but did not specify whom police suspected in the attempt, saying it was under investigation.
"From what we presently know, this was an attempt to crash the plane," Bekri said.
"Because this incident just occurred, questions as to who these people were, where they came from what their goal was, what kind of background, we are currently investigating. Once we've investigated clearly, I believe you will then know," Bekri said.
He said the crew responded and the plane made an emergency landing in the western city of Lanzhou with no damage or injuries. He said it continued to its original destination, Beijing, after about one hour.
A man who answered the phone at China Southern's Urumqi office said the incident was under investigation and had no further details. He hung up without giving his name.
An airline spokesman at its southern hub of Guangzhou refused to answer questions about the incident and said all press inquiries had to be faxed to corporate headquarters.
While Bekri refused to further describe the incident, he prefaced his remarks with a denunciation of Uighur separatists, saying "high-pressure tactics" were the only way of dealing with the problem.
"Those in Xinjiang pursuing separatism and sabotage are an extremely small number," Bekri said.
"They may be Uighurs, but they can't represent Uighurs. They are the scum of the Uighurs."