ATHENS, June 7 -- The apartment on Acharnon Street in the Kato Patisia district of Athens looked like any other rented flat in the middle of a working-class neighbourhood. But when Greek counterterrorism officers entered it on Saturday, they found precision laboratory scales, a magnetic hotplate stirrer, radiation dosimeters, and digital storage devices - the infrastructure of a bomb-making operation at an intermediate stage, waiting only for the chemical precursors the tenant had ordered online and not yet received.

The tenant was already in custody. A 37-year-old Palestinian national, arrested the same evening in Agios Nikolaos on the island of Crete, had been working as a seasonal hotel employee for the past two weeks within a few kil...