The men, aged 28 and 46, had been detained Thursday after police commandos raided an Islamic cultural centre in western Berlin and a building in Britz, a southern suburb of the German capital.
Berlin prosecutors said Friday they were still investigating the two, a Syrian and a Tunisian, and a third suspect, on suspicion they had planned an attack, and were examining digital data carriers in search of evidence.
"We continue to investigate three persons on suspicion of having planned a serious act of violence," Berlin public prosecutors spokesman Martin Steltner told AFP.
The two men were picked up by police Thursday in Britz in the multicultural Neukoelln district, where police also examined a suspicious object in a car that turned out to be harmless.
The searches did not turn up any weapons or explosives.
German media reported officers had acted on a tip-off that an attack in the western city of Dortmund was being planned, as European police forces are on high alert following the jihadist attacks in Paris on November 13 that claimed 130 lives.
A Germany-Netherlands football match in the northern German city of Hanover was called off on November 17 over fears of an attack.
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