Turkey is accusing Germany of supporting the network of a US -based Muslim cleric it blames for last year's attempted coup - comments likely to aggravate a diplomatic feud between the two countries.
He told German news magazine, Der Spiegel: "Turkey has tried to convince us of that at every level but so far it has not succeeded".
Presidential spokesman Ibrahim Kalin said Europe was seeking to "whitewash" Gulen's group, while Defence Minister Fikri Isik said the comments raised questions about whether Berlin itself was involved in the putsch.
The ban on Turkish officials addressing rallies of expatriate Turks in various European countries, including the Netherlands and Germany, has brought relations between Ankara and the EU to a new low.
Turkey's foreign ministry expressed its displeasure to Germany's ambassador in Ankara, according to a statement by the ministry.
Police in Frankfurt, where hundreds of officers were deployed to the event, described the protest as peaceful and said on Twitter that most of the demonstrators had complied with German laws, adding: "We want to guarantee they can exercise their fundamental rights".
Germany hasn't responded to the comments. "Why are they protecting them?"
Turkey lashed out Sunday after Germany's intelligence chief said he was unconvinced by Turkish assertions US-based Islamic preacher Fethullah Gulen was behind the failed coup of July 15. Turkish authorities have blamed the attempted coup that left 248 people dead on the Fethullahist Terrorist Organization (FETÖ), whose leader is Gülen.
Turkey blames Gulen's organisation for the failed coup and been demanding from the USA to return him to Turkey.
Turkey says there is a possibility that Turkish ministers could plan another rally in Germany ahead of an April 16 referendum, a move that could further escalate tensions between Ankara and Berlin.
Gulen, a former Erdogan ally who has lived in self-imposed exile in the United States since 1999, has denied the charges and condemned the coup.
Iyimaya said that certain European countries act in an obvious way against the constitutional changes that will be put into referendum next month.