BERLIN -- German police say one of four Algerian men suspected of plotting an attack in Berlin had registered in Germany as a Syrian refugee and another had contacts in Belgium.

Police, who suspect the four had ties to the Islamic State of Iraq and Syria (ISIS), conducted raids Thursday in Berlin and western Germany. One of the Algerians and his wife were arrested at a refugee home because they were sought by Algerian authorities for belonging to the extremist group.

Berlin police said Friday the man arrived in Germany at the end of last year and sought asylum under a Syrian identity. They said they established that another of the Algerians, who wasn't arrested, had contacts with Belgium. They didn't elaborate, but the country has a strong Islamic extremist scene.

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CBS News reported last month that, according to the latest figures, more foreign fighters have gone from Belgium to join jihadist groups in Syria and Iraq, per capita, than any other European nation.

Last month, Germany's domestic intelligence agency said the number of Islamic extremists heading to Syria and Iraq continues to grow, raising concerns over trained fighters returning who could carry out attacks in Europe.

The agency said its latest evidence shows 790 people so far have made the trip from Germany to link up with militant groups in the Mideast, up from 750 in October, and about one-third had returned.