Berlin, Germany - A 34-year-old US citizen was detained on suspicion of stalking Taylor Swift ahead of the first German concert of her record-breaking Eras Tour, police said on Thursday.

The man was taken into custody on Wednesday evening before the show at the Veltins-Arena in Gelsenkirchen, police in the western city said in a statement.

The alleged stalker had come to the attention of police after making threats against the singer and her boyfriend Travis Kelce on social media, the statement said.

"As initial investigations could not completely rule out the possibility of danger, the suspect was identified and taken into custody at the admission control before the concert, for which he had a ticket," the police said.

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Kelce has attended several concerts during the Eras Tour and was in the arena at Gelsenkirchen on Wednesday night.

The suspect will be detained until Saturday, the police said, adding that there had been no danger to Swift or her fans.

Around 60,000 people attended the first of three sold-out Eras Tour concerts in Gelsenkirchen on Wednesday.

Swift and her entourage will also stop off in Hamburg and Munich before heading to Poland and Austria.