A 17-year-old asylum-seeker has been questioned by German police after concerns were raised that he was planning a suicide attack in Berlin.

Officers in Brandenburg state said the teenager was detained Tuesday in the village of Gerswalde, 60 miles northeast of the capital, after they learned he had sent a farewell message to family members and told them that "he had joined the jihad," or holy war.

The WhatsApp message talking about jihad to the suspect's family was sent within the last week and Brandenburg authorities were told of it late Monday night by two other German states, Brandenburg police spokesman Torsten Herbst told The Associated Press.

He said police had no evidence that a concrete attack was planned. The federal Interior Ministry said it had no indications that an attack had been imminent.

The state Interior Ministry's office identified the suspect as Syrian, but Mr Herbst said investigators were checking to see whether he falsely registered as a Syrian but was actually from a North African country.

The teenager, whose name wasn't released, came to Germany in 2015 as an unaccompanied minor and registered as an asylum-seeker. He has been living since 2016 in a home for minor refugees in Gerswalde, and was detained there in the Tuesday morning raid.

Police said they searched the home and no weapons, explosives or extremist group flags were found. The search turned up three cell phones and a tablet that is believed to belong to the teenager. Investigators were examining the devices.

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The suspect was to be questioned further on Wednesday, and was being kept in detention until then.

German security officials have repeatedly warned that the country is in the sights of international terrorist groups.

Germany saw a number of violent attacks by Islamic extremists last year, including the truck attack on a Berlin Christmas market that left 12 victims dead and dozens of others injured. The attack, carried out by a young Tunisian man who had been denied asylum in Germany, was claimed by Isis.