JAKARTA: The ease with which three separate groups of ethnic Uighur militants sneaked into Indonesia is ringing alarm bells for security forces, who are on high alert for a far deadlier attack than last week’s assault on Jakarta. At least 10 Uighurs, who hail from China, arrived in the world’s most populous Muslim nation over the last 18 months to join radicals, exposing an extensive support network ready to welcome wannabe militants.

Police fear the same network could assist in the return of battle-hardened Indonesian Daesh fighters from Syria, who could then launch more calculated attacks, similar to that which hit Paris last November.

Indonesia’s sprawling archipelago of 18,000 islands is too vast to control the movements of militants, drug smugglers, human traffickers and refugees, police say.

“There is enough security at the main entry points,” the country’s police chief, Badrodin Haiti, told Reuters. “But there are more traditional points for entering illegally, where usually fishermen bring people in.”

With around 500 Indonesians taking one-way trips to join Daesh in Syria and Iraq, authorities had not considered the Southeast Asian nation’s porous border to be a pressing security issue until recently.

But last month’s arrest of an Uighur individual, Ali Mehmet, after police found bomb-making equipment in a house in a Jakarta suburb, spotlighted how easy it is for people to be smuggled into Indonesia.