By Ben Blanchard
BEIJING, July 13 (Reuters) - Poor intelligence and porous borders with Southeast Asia are stymieing China's efforts to stop the flow of ethnic minority Uighur Muslims heading to Turkey, where China says many of them end up fighting for Islamists in Syria and Iraq.
Hundreds, perhaps thousands, of Uighurs keen to escape strife in their far western Chinese homeland of Xinjiang have travelled clandestinely via Southeast Asia to Turkey.
Speaking to Reuters and a reporter from a Singapore newspaper on Saturday, Tong Bishan, a senior police officer who has been helping lead China's efforts to get the Uighurs back, said the Uighurs were mostly crossing into Vietnam and Laos.
Tong, in rare public comment on such a sensitive issue and on the difficulty facing authorities, said he believed the numbers getting out had fallen considerably but it was not possible to stop them completely.
"I've been to the front lines, to the border with Vietnam, it's mountains and rivers. In some places, the border is a little stream, two or three metres wide. Jump over and on the other side it's Vietnam. There's no fence or anything," he said.
Rights groups and exiles have disputed China's account of why the Uighurs are leaving, saying the driving cause is a desire to escape discrimination and Chinese controls on their culture and religion.
The government denies there is a problem with its treatment of Uighurs but hundreds of people have been killed in violence in Xinjiang in the last three years. Uighur militants have been blamed for attacks elsewhere in China.
One Beijing-based diplomatic source said China had been successful at stopping Uighurs from crossing into Central Asia via Kyrgyzstan, after Kyrgyzstan responded to China's request to step up security, and that had led to Uighurs trying to leave via Southeast Asia.
Still, even as security at transport hubs like train and bus stations in Xinjiang has been increased, Uighurs are Chinese citizens and have the right to travel anywhere in the country.
Tong said Uighurs, who speak a Turkic language, were using that right to get to border areas.
"You can't just stop them because they are from Xinjiang or are Uighur. You can't tell from their faces if they are terrorists."
Tong's remarks underscore the intelligence challenge China faces in Xinjiang, where government officials generally do not speak Uighur and where many Uighurs harbour an intense suspicion of the state.
The issue is particularly acute when it comes to China working out exactly how many Uighurs may have ended up in Syria or Iraq fighting for Islamist militants.
Raffaello Pantucci, director of International Security Studies at the London-based Royal United Services Institute, said China had to rely on "friendly agencies" helping them overseas to get intelligence on Uighurs.
"I think that they have been relatively successful in coercing people within China to work with them or for them, but it is not always clear they are able to do that outside," he added.
Western countries have been reluctant to help China, concerned about human rights and doubts over the credibility of China's claims about Uighur militants.
A second Beijing-based diplomat said China had been presenting lists of names of Uighurs it suspected may be in Syria or Iraq to countries in the region asking for help in checking.
"China really does not know who has gone to fight for Islamic State," the source, who has direct knowledge of the situation, told Reuters.
Chinese media has put the number fighting in the Middle East at about 300. The government has not given its own figure for the numbers of Uighurs who have gone abroad, or the number it has managed to have returned.
A source with ties to the Ministry of Public Security said it estimated 10,000 Uighurs had gone abroad in recent years.
The government says some of the 109 Uighurs deported from Thailand back to China last week were on their way to participate in jihad in Syria and Iraq.
Tong said they were in the Xinjiang capital of Urumqi getting health and identity checks. (Additional reporting by Benjamin Kang Lim and Michael Martina; Editing by Robert Birsel)