The authorities in China say they have foiled two plots - one to crash an airliner, and another targeting the Beijing Olympic Games.
China sees the Beijing Olympics as key to its international prestige
Officials said a plane crew prevented an attempt to crash a flight from Xinjiang province to Beijing on Friday. Two passengers are being questioned.
Another official said a raid that saw two people killed in Xinjiang in January foiled a plot on the Games.
Uighur separatists in Xinjiang have waged an insurgency for many years.
The Chinese authorities accuse them of having links to international terror networks
The officials were speaking on the sidelines of the current national parliamentary session.
BBC China editor Shirong Chen, in Beijing, says the fact both incidents have been mentioned on the same day suggests what may be an orchestrated attempt to justify preventative strikes against suspected terrorists in Xinjiang.
As the Beijing Olympic Games draw closer - they start on 8 August - the Chinese authorities become more concerned about possible terrorist attacks against the games, our correspondent says.
They have deployed more security forces in and around Beijing and have stepped up their fight against "terrorism, separatism and extremism".
The alleged airliner plot involved a flight that originated in Urumqi, Xinjiang province, and was bound for Beijing.
The China Southern Airlines plane landed safely despite an attempt "to create an air disaster", said Xinjiang Governor Nur Bekri.
"Who the people involved in the incident were, where they were from, what their aim was and what their background was, we are now investigating," he said.
But he said there was "an attempt to crash the plane", and that the crew responded and brought the plane to an emergency landing in the city of Lanzhou, in neighbouring Gansu province, with no damage or injuries.
Reuters quoted an anonymous source saying inflammable material was found in the plane's toilet, and that at least two passengers on the flight were taken into custody.
There was no confirmation of this.
Meanwhile, the boss of the Communist Party in Xinjiang, Wang Lequan, said January's raid, also in Urumqi, had thwarted a plot to attack the Olympics.
"Their aim was very clear," he said. "Specifically to sabotage the staging of the Beijing Olympics."
"Those terrorists, saboteurs and secessionists are to be battered resolutely, no matter what ethnic group they are from," said Mr Wang.
China has been struggling for years to contain separatist sentiment among the ethnic Uighur minority in Xinjiang.
Some Uighurs have campaigned for the mainly Muslim province to become an independent republic.
The Xinjiang governor, himself an ethnic Uighur, said only a "very small number of people" in the region support the separatists.
"They don't represent the Uighur people," he added.