Turkey is blocking plans by a senior German delegation to visit the Incirlik air base, German officials have said.
Turkey has not commented on why it has not approved the German plans.
The visit had been expected to take place in July.
“The Turkish authorities at the moment are not approving the travel plans,” a German defence ministry spokesman said.
“There is no written statement on the reason.” He added that the delegation, headed by deputy defence minister Ralf Brauksiepe and including other members of parliament, still hoped the trip could go ahead.
Last week, Germany’s defence ministry said it was finalising an agreement with Turkey on building new housing and aircraft facilities for the German troops at Incirlik.
The latest sign of troubled relations between the two Nato allies comes three weeks after the German parliament’s declaration about genocide.