Austrian police have detained a 14-year-old boy for the second time on suspicion of belonging to a terrorist organization, planning to travel to Syria and researching how to build bombs, a police spokesman said on Friday.
The boy from Lower Austria province was first detained in October but released from investigative custody after a few days on condition he remain in contact with authorities.
When his mother reported him missing this week, authorities renewed the arrest warrant.
About 170 people have left Austria to fight with jihadis in the Middle East, according to the Interior Ministry, some of whom have been killed. Fear of attacks is running high in Europe after Islamist gunmen killed 17 in Paris.
Authorities have said the boy had expressed sympathy with Islamic State militants fighting in Syria and Iraq and researched on the internet how to build bombs.
Police picked up the 14-year-old, who authorities have said is a Turkish national, in Vienna on Friday alongside a 12-year-old who will be handed over to his parents as there is no arrest warrant against him, the spokesman said.
Austria last week detained two teenage girls after they tried to travel to Syria to marry Islamic State fighters. They have since been released.