Police in Germany are reportedly searching for an Islamic State bombmaker believed to be at large in the country.

Intelligence services have intercepted phone calls from the wanted man in which he speaks of explosives being ready, but have been unable to identify him, according to Bild newspaper.

Authorities have refused to comment on the report.

Details of the suspect have only emerged in the wake of a bomb attack on a Borussia Dortmund team bus last month.