Turkey was today warned that it risked breaching Nato's membership rules that oblige respect for democracy as President Erdogan's crackdown in the wake of the weekend's coup attempt gathered pace.

John Kerry, the US Secretary of State, and Jens Stoltenberg, the Nato Secretary General, issued the warnings amid a widespread purge of judges and civil servants.

It came as Mr Kerry dug in against Ankara’s demands to hand over cleric Fethullah Gulen, saying the US would only consider an extradition request made on the basis of credible evidence.

“With respect to Nato and the movement of Turkey, Nato also has a requirement with the respect to democracy," Mr Kerry said after meeting EU foreign ministers in Brussels. "Nato will measure very carefully what is happening."

Mr Stoltenberg said: "Being part of a unique community of values, it is essential for Turkey, like all other allies, to ensure full respect for democracy and its institutions, the constitutional order, the rule of law and fundamental freedoms."