The Council of Europe warned Turkey on Monday that restoring capital punishment after an attempted coup would be incompatible with its membership of the pan-European human rights organisation.
"No member state can exercise capital punishment," said Council of Europe Secretary General Thorbjorn Jagland, quoted by a spokesman.
"This is an obligation," he added, stressing that Turkey had ratified human rights protocols which "abolish death penalty under all circumstances".
Turkish President Recep Tayyip Erdogan has vowed to wipe out the "virus" of the putschists after facing down last week's coup bid by elements of the military.
On Sunday Erdogan told supporters that Turkey could consider reintroducing the death penalty, which it had abolished in 2004 as part of its longstanding EU membership bid.
Signed in Strasbourg in 1983, protocol 6 of the European Convention on Human Rights, drafted by the Council of Europe, excludes all capital punishment except in time of war or imminent threat of war.
The convention's later protocol 13, dating from 2002, closes the time-of-war loophole, stating clearly that "no one shall be condemned to such penalty or executed."
Turkey joined the Council of Europe three months after it was inaugurated in 1949.
The death penalty was abolished in Turkey in 2004, as part of the country's bid to join the European Union. Its application has been moving at glacial pace.
Turkey's Erdogan to CNN: Death penalty not ruled out for plotters
Washington (AFP) July 18, 2016 –
Turkish President Recep Tayyip Erdogan has reiterated that the death penalty is not off the table for those suspected of plotting a coup against his government, in an interview with CNN broadcast Monday.
Erdogan, giving his first media interview since Friday's dramatic coup attempt, also said his government would submit a written request for the extradition of US-based Muslim cleric Fethullah Gulen, whom he blames for the unrest, in the coming days.
"There is a clear crime of treason," Erdogan, speaking through a translator, told CNN when asked about calls for the alleged plotters to face capital punishment.
"But of course, it will take a parliamentary decision for that to take action in the form of a constitutional measure," he said, given that Turkey abolished the death penalty in 2004 as part of its long-standing efforts to join the European Union.
"So the leaders will have to come together and discuss it. If they accept to discuss it, as the president, I will approve any decision to come out of the parliament."
Turkey launched fresh raids and sacked almost 9,000 officials Monday in a relentless crackdown against suspected coup plotters, with Erdogan vowing to wipe out the "virus" of the putschists after Friday's coup attempt, which left more than 300 dead.
But the United States and European Union have sternly warned him against excessive retribution and to respect the rule of law.
Erdogan has blamed the coup attempt on Gulen, his arch-enemy, who lives in self-imposed exile in Pennsylvania. Gulen has denied any involvement.
The Turkish leader told CNN that his country's formal request for extradition would soon be submitted.
"We have a mutual agreement of extradition of criminals," he told the network.
"There should be reciprocity in these types of things."