A leading German politician says the government shouldn't allow voting in Germany in a possible referendum on whether to reintroduce the death penalty in Turkey.

Turkish President Recep Tayyip Erdogan has spoken of reinstating the death penalty since narrowly winning expanded powers last month. Germany and other European countries vehemently oppose executions.

Germany's Foreign Ministry has noted that the government must approve sovereign actions by other countries, such as referendums, on its territory. It permitted polling stations for Turkish nationals in last month's Turkish constitutional referendum.

Martin Schulz, Chancellor Angela Merkel's challenger in September elections, told Der Spiegel magazine Friday: "We cannot allow voting in Germany on an instrument that contradicts our values and our constitution."

Schulz's center-left party is the junior partner in Merkel's current coalition government.