President Tayyip Erdogan on Monday called on Turkish voters in Europe to defy the "grandchildren of Nazism" and back a referendum this month on changing the constitution, comments likely to cause further ire in Europe.

Erdogan has repeatedly lashed out at European countries, including Germany, in campaigning for the referendum, accusing them of "Nazi-like" tactics for banning his ministers from speaking to rallies of Turkish voters abroad.

Germany has been incensed by the references to its wartime past. German Chancellor Angela Merkel has said that the references must stop.

Erdogan also said he would take the issue of whether Turkey should restore the death penalty to referendum if necessary. Turkey abandoned capital punishment more than a decade ago as part of its bid to join the European Union. Restoring capital punishment - which crowds have called for following the July 15 failed coup - would all but end Turkey's bid to join the EU, officials from the bloc have said.

Erdogan made the comments at a rally in the Black Sea province of Rize.