Berlin police said they had released two men on Friday who were suspected of planning an attack and had been arrested on Thursday evening in connection with a search at an Islamic cultural center in the German capital.
The German newspaper Tagesspiegel, citing security sources, said the two men from Syria and Tunisia had links to Islamic State, which may have been planning an attack in the western city of Dortmund,
But Interior Minister Ralf Jaeger of North-Rhine Westphalia, the regional state in which Dortmund is located, told local newspaper Ruhr Nachrichten that there were no concrete indications of planned attacks in Dortmund.
Criminal investigations have also been opened into other people, including asylum seekers, in connection with Thursday's arrests, the newspaper said.
The Berlin prosecutor's office, now in charge of the investigation, did not respond to requests for comment from Reuters.
Chancellor Angela Merkel said on Wednesday the security threat level in Germany remained high after the Paris attacks on Nov. 13 where 130 people were killed.
On Thursday, an object "presumed to be hazardous" was found in a car used by the two main suspects, prompting police to block off the area and evacuate residents from several buildings, according to a police statement.
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