BEIJING — Chinese police killed alleged terrorists plotting to attack the Beijing Olympics, while a flight crew managed to prevent an apparent attempt to crash a Chinese jetliner in a separate case just last week, officials said today.

The top Communist Party official in the western region of Xinjiang, Wang Lequan, said materials seized in a January raid in the regional capital, Urumqi, had described a plot with a purpose “specifically to sabotage the staging of the Beijing Olympics.”

“Their goal was very clear,” Mr. Wang told reporters in Beijing.

Mr. Wang cited no other evidence 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 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.

China has ratcheted up anti-terror preparations ahead of the August Games, with the nation’s top police official last year labeling terrorism the biggest threat facing the event.

Police found guns, homemade bombs, training materials, and “extremist religious ideological materials” during the January 27 raid in Urumqi, in which two members of the gang were killed and 15 arrested, according to earlier reports.

Chinese forces have for years been battling a low-intensity separatist movement among Xinjiang’s Uighurs, a Turkic Muslim people culturally and ethnically distinct from China’s Han majority. Iron-fisted Chinese rule has largely suppressed the violence, however, and no major bombing or shooting incidents have been reported in almost a decade.

Mr. Wang said the group had been trained by and was 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 both the United Nations and America. East Turkestan is another name for Xinjiang.

China says its main terror threat comes from ETIM. Although the group is not believed to have 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.

Mr. Wang said security forces would take pro-active measures to crush terrorism, religious extremism, and separatism.

“These guys are fantasizing if they think they can disrupt the Olympics,” Mr. Wang, known for his hardline stance on crushing dissent, said. “They don’t have the strength.”

Few details were available about the alleged attempt to crash the China Southern Airlines flight that left Urumqi at 10:35 a.m. on Friday.

Mr. Bekri, the governor of the Xinjiang region, indicated that more than one person was involved, but did not specify who was suspected to be behind the attempt, saying it remains under investigation.