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.