Norbert Lammert expressed the outrage in Germany's lower house of parliament, the Bundestag, on Thursday, over comments made by Turkish President Recep Tayyip Erdogan. Lammert also denounced the "sometimes hate-filled threats and smears" targeting the 11 German lawmakers with Turkish heritage.

"I would not have thought it possible in the 21st century that a democratically elected head of state would criticize members of the German Bundestag by voicing doubts about their Turkish heritage, by labeling their blood as impure," Lammert told parliament on Thursday.

Germany's large Turkish diaspora has protested the resolution on Armenia

He was criticizing Erdogan's reaction to last week's contentious Bundestag resolution, which repeatedly referred to the killings of Armenians in Ottoman-era Turkey during World War I as genocide. Turkey disputes this definition of the massacre of Armenians.

Erdogan had said the German-Turkish parliamentarians were a "mouthpiece for the PKK," the outlawed Kurdistan Workers' Party seeking an independent Kurdish state. The president also suggested that the 11 lawmakers should undergo blood tests to see "what kind of Turks they are."

"Also, I reject in all its forms the insinuation that members of this parliament are terrorist mouthpieces," Lammert said.

EU rebuke follows in writing

European Parliament President Martin Schulz, a German Social Democrat, also wrote an open letter to Erdogan, saying differences of opinion among elected officials should not prompt allegations of terrorist sympathies.

"Such an act constitutes a complete breach of a taboo, which I condemn as strongly as possible," Schulz wrote. "As the president of a multi-national, multi-ethnic and multi-faith parliament, allow me to make the following point: MPs' freedom to carry out their mandate as they see fit is a fundamental pillar of our European democracies."

German-Turkish MPs, not least Cem Özdemir (l.), who is now under police protection, have also stood up on other issues like media repression in Turkey

Turkey is one of several countries recognized as a candidate for potential EU membership one day. Schulz sought to defend both German MPs and those in Turkey opposed to Erdogan's policies.

"A string of the German Bundestag MPs you have personally attacked, but also Turkish parliamentarians affected by measures which you support, are amongst longstanding colleagues of mine; some of them are very close to me personally," Schulz said. "I feel obliged to protect these colleagues wherever I can."

'Unequivocal' message after Merkel's 'incomprehensible' one

German-Turkish MPs have since reported a wave of criticism, trolling and even death threats in the wake of last week's vote. Some have been placed under police protection. Sevim Dagdelen of the Left party told DW on Wednesday that she had been told to "take a holiday in Buchenwald," the World War II concentration camp, with another saying there was a bounty on her head.

Lammert told parliament that these threats and smears had in some cases been encouraged by "high-ranking Turkish politicians."

"We will face up to any criticism. We will even tolerate personal attacks and polemics," the house speaker said. "But anybody who tries to exert pressure on a parliamentarian using threats must know this: They are attacking the entire parliament."

Lammert said that all party leaders in parliament had appealed to him "to voice our collective position once again, unequivocally."

Interior Minister Thomas de Maiziere, the next to speak after Lammert, thanked his CDU ally "most sincerely" for his "clear words." Chancellor Angela Merkel had faced criticism for her response to the issue on Tuesday, when she described the threats against German MPs as "incomprehensible."

Critics argued that Merkel should have formulated a more emphatic rejection of the behavior. Turkey and Germany have been in close, tense consultations in recent months over measures to deal with the so-called refugee crisis.

The Bundestag had initially scheduled a special debate at the request of the Left party, to address this issue later on Thursday. The Left subsequently withdrew its request, saying Lammert's statement had satisfactorily covered the issue.