By Christian Levaux VERVIERS, Belgium (Reuters) - Belgian police killed two men who opened fire on them during one of about a dozen raids on Thursday against an Islamist group that federal prosecutors said was about to launch "terrorist attacks on a grand scale". Coming a week after Islamist gunmen killed 17 people in Paris, the incident fueled fears across Europe of young Muslims returning radicalised from Syria. A third man was detained in the eastern city of Verviers, where police commandos ran into a hail of gunfire after trying to gain entry to an apartment above a town center bakery. All three were citizens of Belgium, which has one of the biggest concentrations of European Islamists fighting in Syria.