JAKARTA (Reuters) - Indonesian authorities are working with their counterparts in China to stem a flow of ethnic Uighur militants seeking to join Islamist jihadists in the world’s most populous Muslim country, Indonesia’s counter-terrorism chief said.

Saud Usman Nasution, the head of the National Counter-Terrorism Agency, gestures during an interview at his office in Bogor, January 5, 2016. REUTERS/Beawiharta

Saud Usman Nasution’s comments come amid mounting concern in Indonesia about possible attacks by sympathizers of the Islamic State group and follows the arrest of 13 men across the island of Java, including a Muslim Uighur with a suicide-bomb vest.

The appearance among Indonesian militant networks of Uighurs, who come from the Xinjiang region in far-western China, is likely to add to Beijing’s concerns that exiles will return to their homeland as experienced and trained jihadists.

China says Islamist militants and separatists operate in energy-rich Xinjiang on the borders of central Asia, where violence has killed hundreds in recent years.

Rights groups say much of the unrest can be traced back to frustration at controls over the Uighurs’ culture and religion, and that most of those who leave are only fleeing repression not seeking to wage jihad. China denies repressing rights.

Nasution, who heads the National Counter-Terrorism Agency, told Reuters in an interview on Tuesday that several Uighurs had responded to a call last year by Santoso, Indonesia’s most high-profile backer of Islamic State, to join his band of fighters.

Islamic State and human trafficking networks helped them travel via Myanmar, Thailand and Malaysia to Santoso’s hideout in an equatorial jungle of eastern Indonesia, he said.

However, the would-be suicide bomber arrested on Dec. 23 was hiding in a house just outside the capital, Jakarta.

“We are cooperating with China and investigating evidence such as ATM cards and cellphones,” Nasution said, adding that an Indonesian team went to China to interview members of the man’s family, who would not confirm that they were related to him.

There was no immediate comment from China’s foreign ministry on whether Beijing is collaborating with Indonesia.

“As far as China is concerned, these people are running off, some of them taking part in jihad and planning to strike back,” said Pan Zhiping, a terrorism expert at the Xinjiang Academy of Social Sciences.

“Of course we must stop them. I believe, in terms of jointly guarding against extremism, it is necessary that we cooperate.”

Bilveer Singh of the Rajaratnam School of International Studies in Singapore said the direct involvement of Chinese Uighurs in Southeast Asian militancy added “an external dimension to the existing home-grown terrorist threat”.

“It could also complicate ties with a rising China, which may want to play a bigger counter-terrorism role in the region,” Singh said in a Eurasia Review article.

‘SERIOUS CONCERN FOR CHINA’

Indonesia’s security forces have given Santoso, who styles himself as the commander of the Islamic State army in Indonesia, until Jan. 9 to surrender along with his force of about 40 men on the far-flung island of Sulawesi.

However, security analysts believe a larger threat is emerging across the populous island of Java as networks of support for Islamic State grow.

Indonesia has been largely successful in disrupting domestic militant cells since the bombing of two nightclubs on the resort island of Bali in 2002, and sporadic attacks have been mainly targeted at the police.

The government is now worried that the influence of Islamic State, whose fighters hold swathes of territory in Syria and Iraq, could bring a return of jihadi violence and strikes against foreigners and soft targets.

Officials believe there are more than 1,000 Islamic State supporters in Indonesia, and say that between 100 and 300 have returned from Syria, though this includes women and children.

Nasution said that monitoring of radical groups had revealed plans to launch attacks on Christmas Eve and around the New Year holiday but the situation was now under control.

“They cannot attack like in the Middle East or Europe because we anticipate before they attack. We monitor their activities every day,” he said. “Their capability has not increased because their personnel is limited, their funding is limited and explosives are limited.”

Police spokesman Suharsono said the Uighur arrested just outside Jakarta was part of an Islamic State-affiliated group based in the Central Java city of Solo.

Officials declined to comment on media reports that two other Uighurs from the same group were on the run, but they did confirm that three Uighurs were with Santoso.

Four others were sentenced last year to six years in prison for conspiring with Indonesian militants.

Todd Elliott, a Jakarta-based terrorism analyst for Concord Consulting, said many Uighurs will see Indonesia as more accessible than Turkey or Syria and are exploiting entrenched smuggling and human-trafficking networks to travel around the region undetected.

“I am sure returning Uighur fighters are a serious concern of the Chinese government,” he said, adding that Islamic State’s hardline ideology has gained traction among small minorities in both Xinjiang and Indonesia, binding them closer together.