The comment was made by Ibrahim Kalin, a spokesman to President Recep Tayyip Erdogan, in an interview with broadcaster CNN Turk on March 19.
Turkey is accusing Germany of supporting the network of a USA -based Muslim cleric it blames for last year's attempted coup - comments likely to aggravate a diplomatic feud between the two countries.
"It is impossible to explain for German authorities to claim that Turkey's elected representatives' meeting with their citizens is risky, but to treat terrorists as legitimate actors", Kalin added. "Because these are useful instruments for Germany to use against Turkey".
Turkish officials have been further angered over the weekend after Bruno Kahlmade, the German foreign intelligence chief, said Turkey "failed to convince" Germany that the organisation of Fethullah Gulen, a religious leader and businessman who is in a self-imposed exile in the U.S., was directly behind last year's coup attempt. Turkish authorities have blamed the attempted coup that left 248 people dead on the Fethullahist Terrorist Organization (FETÖ), whose leader is Gülen.
Turkey's foreign ministry expressed its displeasure to Germany's ambassador in Ankara, according to a statement by the ministry.
"Turkey has tried to convince us of that at every level but so far it has not succeeded", Kahl was quoted as saying by the "Spiegel" news magazine.
"It's an effort to invalidate all the information we have given them on FETO".
On Wednesday German foreign ministry spokesman Martin Schaefer said the government had approved voting by the estimated 1.4 million Turkish nationals living in Germany who are eligible to cast ballots in the April 16 referendum.
Ankara blames Gulen's network of followers in the military for a failed coup attempt in July, when a group of rogue soldiers seized tanks, helicopters and war planes to attack parliament and attempt to overthrow the government.
Tens of thousands of people were arrested and civil servants were sacked in the purges after the coup attempt.
Erdogan and the Turkish government want the United States to extradite Gulen, who denies involvement in the coup attempt.
Iyimaya said that certain European countries act in an obvious way against the constitutional changes that will be put into referendum next month.