Germany’s president said he was "scared" by recent developments in Turkey during a visit to the country on Monday, saying "the rule of law is in danger" from its efforts to muzzle opposition.

Germany's president said he was "scared" by recent developments in Turkey during a visit to the country on Monday, saying "the rule of law is in danger" from its efforts to muzzle opposition.

"I ask myself if judicial independence is still guaranteed if the government purges so many prosecutors and police, and prevents them from shedding light on crooked developments... or manipulates decisions in its favour," said President Joachim Gauck during a speech at the Middle East Technical University in Ankara, part of a four-day visit to Turkey.

Gauck was keen to emphasise that he still sees a European future for Turkey, but did not pull his punches in commenting on the recent actions of Turkish Prime Minister Recep Tayyip Erdogan, who has been accused of increasingly authoritarian responses to street protests and a wide-ranging corruption scandal.

"We hear many voices expressing disappointment, resentment and anger over the government's policies, for example when there is interference in how they should live, when more powerful control over the secret service is proposed, and when street protests were quashed by force and people even lost their lives.

"I must confess that these developments are scaring me," said Gauck, who held a meeting with Erdogan earlier in the day.

Gauck said he had no desire "to interfere in domestic affairs" but "as a democrat, I will raise my voice whenever I see the rule of law is in danger."

He called on the Turkish leadership to uphold human rights, saying "a pro-freedoms and democratic Turkey which is committed to European values will be a model for neighbouring and Arab countries".

Turkey began talks on joining the EU in 2005 but its path has been stalled by opposition from existing members and, increasingly, by concerns over Erdogan's policies.

"Does Twitter and YouTube have to be banned? Why does such a powerful government interfere in the judiciary or the media?" Gauck asked at a news conference earlier in the day, referring to Erdogan's recent moves to ban social media and increase government control over the courts amid the widening graft scandal.

Erdogan's crackdown on the media and judiciary is driven by his concern that a "parallel state" orchestrated by powerful US-based cleric Fetullah Gulen is responsible for the corruption probe and other attempts to undermine his government.

"I don't think the government is under threat. It is a strong government which has won legitimacy with the elections," said Gauck, referring to Erdogan's latest emphatic win in local elections last month.

Germany opposes Turkey's full membership in the EU and instead hopes to establish a "privileged partnership" -- an option that Ankara categorically rejects.