BEIJING: Police in the southwestern Chinese border province of Yunnan have shot dead four militants and found 553 people attempting to flee the country since 2014, state media said on Friday, giving more details of efforts to stop ethnic Uighurs leaving China.

The report comes as China steps ups efforts to bolster its claims that some of the 109 Uighurs deported from Thailand back to China last week posed a security threat, amid global concern about their wellbeing.

Hundreds, perhaps thousands, of Uighurs, a largely Muslim ethnic minority that calls Xinjiang home, have left China in recent years, clandestinely crossing into Southeast Asia before making their way to Turkey.

Rights groups say such migrants are mostly fleeing ethnic violence in Xinjiang and Chinese controls on their religion and culture. Hundreds of people have died in unrest in Xinjiang in the last three years, blamed by Beijing on Islamist militants.

Beijing says many of those fleeing are extremists hoping to join up with other militants in Iraq and Syria. It denies any repression in Xinjiang.

In a detailed report of foiled attempts to leave the country since 2014, the Yunnan police said that they had mounted a "swift and fierce attack" and "shot dead four violent terrorists", according to the official China News Service.

In one incident in March, Chinese police on the Vietnamese border shot dead a suspect "madly holding a knife to attack police and carry out so-called holy war", the report said.

A second suspect from the same group was killed the next month, after a search involving some 10,000 police and helicopters, it added.

The account did not mention the ethnicity of the suspects, but the language used is typical of how China talks about what it says are Uighur extremists.

In another case in January, police seized 30,000 yuan ($4,831.54), two cars and mobile phones from a group which was planning to join al Qaeda, the report said.

"One of them, a woman, crazily attacked police with a dagger which was on her person, and was subdued on the scene."

Yunnan borders Vietnam, Laos and Myanmar, and the remote, mountainous border there is very porous, which the government has admitted has hampered efforts to stem the outflow.

Yunnan is a particularly sensitive place due to an attack at a train station in provincial capital Kunming last year in which 31 people were killed and 141 injured. Police shot dead four of the attackers, who were all Uighurs.

China is home to about 20 million Muslims spread across its vast territory, only a portion of whom are Uighurs.