BEIJING (Reuters) - Chinese police shot dead two ethnic Uighurs trying to cross the border with Vietnam, state media said on Monday, as the public security ministry accused a separatist group of orchestrating hundreds of cases of human smuggling.

Hundreds of people have been killed around China in the past two years in violence between majority Han Chinese and Uighurs, a Muslim minority from China's western Xinjiang region.

Chinese authorities say they worry that Uighurs go abroad to link up with Islamist militants, but human rights groups say Uighurs are fleeing persecution under harsh government policies.

A "conflict" occurred when the Uighurs "violently resisted arrest" near a highway tollbooth on Sunday night in Pingxiang city in the southern region of Guangxi, the China News Service said.

"Police ultimately shot dead two people, and one person fled toward a residential community," the news agency cited local authorities as saying.

It gave few details of the incident, but said armed police had mounted a city-wide search for the man who fled.

The flow of Uighurs across China's porous southern border has swelled in recent years and groups have surfaced in Southeast Asia seeking political asylum.

On Sunday, China's Ministry of Public Security said that since May, a task force on human smuggling across the country's southwestern borders had uncovered 262 cases.

The smuggling is "mainly organized abroad and controlled behind the scenes by the East Turkestan Islamic Movement (ETIM) in efforts to spread religious extremism, and bewitch and incite people to flee abroad to take part in jihadist activities," the ministry said in a statement on its website.

The "4-29" task force, deployed to the provinces and regions of Henan, Guangdong, Guangxi, Sichuan, Yunnan and Xinjiang, had captured 852 suspected border crossers and 352 suspects who had plotted or transported people, the ministry said.

State media have said as many as 300 ETIM members are traveling to Syria via Turkey to join the Islamic State.

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The government says ETIM wants to create its own state called East Turkestan, but many foreign experts doubt it exists as a cohesive group.

Instead, human rights advocates argue that economic marginalization of Uighurs and curbs on their culture and religion are main causes of ethnic violence.

"There is a direct link between the dramatic increase of runaways and China's policy of suppression," Dilxat Raxit, the spokesman for the exiled World Uyghur Congress, said in an email.

(Reporting by Michael Martina; Editing by Clarence Fernandez)