"Nearly every day we are seeing new measures that flout the rule of law and that disregard the principle of proportionality," government spokesman Steffen Seibert told reporters. "There is no doubt that they are deeply worrying."
Turkish President Recep Tayyip Erdogan on Wednesday chaired a crunch security meeting for the first time since the failed coup, after a widening purge that has seen around 50,000 people either detained or sacked.
Ankara says the coup was masterminded by US-based preacher Fethullah Gulen and the massive crackdown appears to be targeting individuals suspected of any connection to Erdogan's ally-turned-foe.
The purges have stoked alarm that Erdogan was using the coup plot to crack down on opponents, with Turkey's Western allies urging the authorities in the strategic NATO state to obey the rule of law.
Germany had already issued a sharp warning to Turkey Monday, blasting "revolting scenes of caprice and revenge" after the failed putsch and warning it against reinstating the death penalty.
After Erdogan said on Sunday that Turkey would consider a return of capital punishment, Seibert said such a move "would mean the end of EU membership talks". Turkey abolished the death penalty in 2004 under reforms aimed at obtaining European Union membership.
Reinstatement would create further issues between the EU and Ankara in the already stalled membership talks.
Germany has the largest ethnic Turkish community outside Turkey with some three million members.
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