MADRID (AP) — Officials say police have arrested a Spaniard suspected of preparing to carry out a suicide attack for the Islamic State group.

An Interior Ministry statement said the man, arrested Tuesday in the central city of Segovia, had traveled to conflict zones in Afghanistan and Syria. It said he had become increasingly radical recently and had tried to obtain material to carry out a suicide attack on transport systems.

It said he was self-taught in jihadi religious extremism and actively promoted the Islamic group on internet social networks.

The ministry said the detainee, from the Basque city of Irun, served time in jail for the killing of a Frenchman in 1984.

The ministry says Spanish police have arrested 173 suspected jihadi activists since 2015.