Despite a police crackdown, unrest in China's northwestern territory of Xinjiang appears to have intensified, fomented by ethnic tensions, strong-arm Chinese tactics and the pull of Islamic fundamentalism.

Armed Uighur militants and Chinese security forces clashed early this month in the isolated town of Aksu, sources said in Beijing. Several militants were killed in what sources here described as a dramatic shootout when Chinese security forces in helicopters clashed with militants who had kidnapped five police officers.

The state-run Xinjiang Daily reported last week that five militants have been sentenced to death for separatism, murder, robbery and illegally dealing in weapons and ammunition in connection with a two-year spate of separatist activities across the vast territory. Eight other separatists got long jail terms, said the paper, which was seen in Beijing today. One of those sentenced to death had killed a police officer.

A classified circular issued in December by the Ministry of State Security, meanwhile, indicated strongly that China believes problems with Uighurs--mostly Muslims with a Turkic language and ethnically different from the majority Han Chinese--will not go away. Sources said the circular ordered security agents to prepare to report on attempts to infiltrate China by Islamic militants from Saudi Arabia, Iran, other Persian Gulf Arab states, Turkey and India. It further instructed Chinese agents to be vigilant about reporting on the movement of weapons into China by militant bands and on plans for attacks against Chinese facilities.

The Aksu clash, last week's sentencing report and the security circular were seen as indications the Uighur struggle against Chinese rule has not been crushed despite a massive troop presence in Xinjiang and the movement of millions of Han Chinese into the region.

These developments also show that while the fight against China's rule over Tibet attracts more international attention, the violent nature of the Uighur separatist movement has become a headache for the Chinese government. The persistence of the Uighur campaign, despite its lack of a charismatic leader like the Tibetan Dalai Lama, also explains to some extent China's staunch support of Russia's operation to crush Islamic rebels in the breakaway region of Chechnya.

Chinese officials said they have strong reason to suspect that Uighur separatists receive help from abroad. One example occurred March 7, 1997, when a bomb planted in a Beijing bus killed two people and injured about eight others. The attack was the first terrorist incident in Beijing since China's revolution in 1949.

After the blast, an Istanbul-based group called the Eastern Turkestan Freedom Organization, made up of exiled Uighurs, claimed responsibility for the attack. Chinese government officials at the time denied that the blast was connected to a separatist organization.

Subsequently, Chinese security officials asked for Israeli assistance in analyzing the explosives used to blow up the bus, a source said. The explosives turned out to be export-grade goods manufactured in China, he said. Further analysis indicated that the explosives had been exported to Pakistan and then re-exported to Afghanistan.

The source, a Middle Eastern businessman and an expert on security matters, said Chinese officials believe that Uighur separatists obtained the explosives from elements within Afghanistan who are interested in pushing Islamic fundamentalism in northwestern China.

Straddling the ancient Silk Road, Xinjiang was brought into the Chinese empire during the Qing dynasty. It is populated by a mix of ethnic groups, including an estimated 8 million Uighurs. In 1944, during the chaos of war with Japan, Uighur leaders declared the sovereign state of East Turkestan, but in 1950, the Communist People's Liberation Army crushed their independence.

In recent years, separatist sentiments in Xinjiang have been fueled by the 1991 collapse of the Soviet Union, the realignment of Central Asia's newly independent Muslim states and the growing pull of Islam. The biggest publicly known separatist action occurred in February 1997 in Yining, near the Kazakhstan border in China's far west. There hundreds of Uighurs shouting, "God is great" and "independence for Xinjiang" took to the streets before authorities cracked down. By official count, 10 people were killed, but Uighur exile groups put the death toll at more than 100.

Like Yining, Aksu has been a hotbed of anti-Chinese sentiment. Sources said the latest round of violence broke out there between Jan. 5 and Jan. 8, when rebels kidnapped the police officers. While details were sketchy, the sources said security forces located a rebel hideout and attacked it, freeing the police officers and killing several rebels.