BEIJING — China executed two members of a Muslim minority today after finding the men guilty of killing 17 police in an attack last year in the country’s far west that Beijing said was an attempt to sabotage the Beijing Olympics.

An overseas activist group called for an investigation of the men’s trial and allegations that they were tortured in custody.

The executions in China’s Xinjiang region came a day after two Tibetans were sentenced to death for arson during riots in Lhasa last spring, showing the government’s determination to tamp down unrest in regions that have chafed under its rule. An overseas group said security has been tightened in cities in Xinjiang with house-to-house searches of residents.

The attack on police last August in the city of Kashgar near the border with Pakistan and Afghanistan was the most brazen of several in the weeks around the Olympics, marring what the government and many Chinese hoped would be a showcase of China as a modern power.

Abdurahman Azat and Kurbanjan Hemit were convicted in December of ramming a truck into a group of police and then lobbing bombs at the officers and stabbing them on Aug. 4, four days before the start of the games, according to the court.

Both were members of the Uighur ethnic group, a Turkic Muslim group that is culturally distinct from China’s majority Han. Militant Uighurs have waged a simmering, sometimes violent separatist rebellion in Xinjiang. Chinese authorities say the militants are influenced and trained by Islamic terrorist groups in Central Asia and the Middle East.

Before the attack, Azat, a vegetable peddler, and Hemit, a taxi driver, wrote a letter saying they had to wage “holy war” and their mission was more important than their lives and mothers, the government’s Xinhua News Agency quoted a local Communist Party official as saying in August.

Officials in Kashgar held a rally at a sports stadium today to read out the supreme court’s approval of the death sentences against the two, Xinhua and a court official said.

An overseas rights activist said local Uighurs who attended the rally informed him by telephone that Hemit’s face was badly swollen and he appeared unable to stand on his own, making them suspect he had been tortured in custody.

“The international community should investigate this and also look into whether these men had access to lawyers. We fear they were not given a fair trial,” said Dilxat Raxit, spokesman for the German-based World Uighur Congress, a pro-independence group.

Court and police officials in Kashgar said they knew nothing about the case when asked to comment on Dilxat’s claims.

Xinhua said 4,000 people watched as the approval of the death sentences was announced. Immediately afterward, the two were executed at another location, said the official from the Kashgar Intermediate People’s Court, who refused to give his name.

Xinhua did not say whether the two prisoners were present at the rally or how they were put to death.

China traditionally carries out executions with a bullet fired at the condemned person’s head, but in recent years also has used lethal injections.

Last year’s violence prompted a clampdown in which the government says 1,295 people were arrested in Xinjiang for state security crimes, compared to a nationwide total of 742 arrests on such charges in 2007.

The Washington-based Uyghur American Association said in a statement today that a security clampdown was under way in the mostly Uighur cities of Kashgar and Hotan, including house-to-house searches, arrests and security checks. China fears possible unrest as the 60th anniversary of the founding of the People’s Republic of China comes up in October, marking Beijing’s assumption of direct control over the region, the group said.