Twenty protesters from China\'s minority Uighur community were killed in a clash with police in the ethnically tense northwestern region of Xinjiang, a Uighur exile group said Tuesday. State media quoted an official in the region calling Monday\'s clash a \"terrorist\" attack and said four people including a police officer were killed when a crowd set upon a police station in the remote city of Hotan. But Uighur activists called it an outburst of anger by ordinary members of the mainly Muslim ethnic minority, and accused authorities of attempting to block information on the deadly incident. The Germany-based World Uyghur Congress, citing sources in Xinjiang, said security forces beat 14 people to death and shot dead six others during the unrest. \"The Chinese authorities should immediately cease their systematic oppression to prevent a further escalation of the situation,\" said Dilxat Raxit, a spokesman for the group. Xinjiang has been plagued by violent unrest in recent years, culminating in savage Uighur attacks on members of China\'s dominant Han group in the regional capital Urumqi in July 2009. Raxit said the latest incident erupted after a group of Uighurs tried to seize a number of police officers as leverage in their demands for the release of family members detained previously. The attackers also set fire to the police station, located near the city\'s bustling bazaar, reports said. The situation in Hotan, an ancient oasis trading post on the famed Silk Road, remained tense after the attack, with police sealing off roads in and out of the city and \"large numbers\" of anti-Chinese flyers circulating, Raxit said in an emailed statement. The flyers demanded the release of detained people, rejected the growing influence of the Han and called for independence, he said. Xinjiang -- a vast, arid but resource-rich region bordering Central Asia -- is home to more than eight million Turkic-speaking Uighurs. Many are unhappy with what they say has been decades of repressive rule by Beijing and unwanted Han immigration. The government says nearly 200 people were killed and 1,700 injured in the 2009 riots in Urumqi -- China\'s worst ethnic violence in decades -- which shattered the authoritarian Communist Party\'s claims of harmony and unity among the country\'s dozens of ethnic groups. China threw a huge security clampdown on Xinjiang after the violence and many Uighurs are angry over the arrests or alleged disappearances of people rounded up across the region in the aftermath. In Hotan, at least 70 people have been detained after Monday\'s incident and authorities were continuing to hunt down other suspects, Raxit said. Police and government staff in Hotan declined to comment on the situation there Tuesday. The China Daily newspaper said two civilians who were taken \"hostage\" in the assault on the police station were among the dead. Xinhua has quoted police saying security forces also shot and killed an unspecified number of attackers. Raxit said 15 people were hurt, three of them seriously. China has seen similar large-scale anti-Chinese protests or rioting by Tibetans in 2008, and by ethnic Mongols in the northern Inner Mongolia region in May this year. In March 2008, authorities in Hotan, which also is variously known as Khotan or as Hetian in Chinese, said extremist forces tried to incite an uprising in a marketplace. Uighur exiles said up to 1,000 people were involved in two protests.