Turkey condemned as incitement to violence an art installation in front of the German Chancellery that portrayed President Tayyip Erdogan as a dictator, days before he is due to attend a G20 summit in Germany.

Turkey's foreign ministry, whose relationship with Berlin has soured in the past year over disagreements on a range of political and security issues, said the matter was made graver by the failure of German police to intervene.

A Reuters TV video of the installation showed a black car draped with a black-and-white banner printed with pictures of Erdogan, Russian President Vladimir Putin and Saudi Arabia's King Salman bin Abdulaziz.

The banner was emblazoned with the phrase "Do you want this car? Kill dictatorship".

Critics in Turkey and overseas accuse Erdogan of authoritarian government, citing a purge of thousands of state officials and many arrests following a failed coup last July. Erdogan says the actions are necessary to ensure stability following the putsch attempt that killed more than 240 people.