Berlin - Germany has frozen all arms deliveries to Turkey, a newspaper reported Friday, after the recent arrests of human rights activists by Turkish police. Berlin stepped up its travel advisory for Turkey on Thursday and warned it would review state guarantees for foreign investment there, measures which Ankara labelled "blackmail and threats." As part of a sweeping overhaul of bilateral ties, Germany is also "freezing all planned and ongoing arms deliveries to Turkey," the top-circulation Bild newspaper reported without citing a source. Chancellor Angela Merkel's right-hand man, Peter Altmaier, did not confirm or deny the report in a ZDF television interview but warned that "we will at any time consider whether further measures are necessary." Relations between Turkey and Germany, home to three million Turks, have been badly strained, particularly since a failed coup a year ago against President Recep Tayyip Erdogan. In the months after the July 2016 coup attempt, Germany already blocked 11 separate arms export shipments to Turkey, including handguns, ammunition or weapons components, according to media reports. Relations sharply deteriorated after a Turkish court Tuesday ordered six rights activists should remain in custody for allegedly aiding a "terror" group, among them German citizen Peter Steudtner.