German Defence Minister Ursula von der Leyen chats with soldiers during a visit of the German Armed Forces Bundeswehr at the air base in Incirlik, Turkey, January 21, 2016.(Xinhua/Reuter photo)

ANKARA, May 15 (Xinhua) -- German lawmakers' visit to Turkey's Incirlik air base where German troops stationed as part of the anti-IS coalition was "inappropriate," Turkey's diplomatic sources said on Monday.

The sources said that the German lawmakers' visit to the military base was "considered inappropriate for the time being," state-run Anadolu Agency reported without elaborating.

Some 250 German troops are stationed at Incirlik as part of the fight against Islamic State (IS) group in neighboring Syria, according to German military.

The Incirlik air base in south Turkey is now used by the U.S.-led coalition launching airstrikes in Syria and Iraq against IS.

Relations between Germany and Turkey were strained in the run-up to Turkey's April 16 referendum, when Germany banned Turkish officials from addressing rallies of expatriate Turks.

In 2016, Turkey banned German lawmakers from visiting the air base for months as a response to German parliament declaring the 1915 killings of Armenians under Ottoman rule a "genocide," which term Ankara denies.