German lawmakers have landed at Incirlik air base to visit German troops supporting the campaign against the Islamic State group.

Turkey had long refused to allow German lawmakers to visit personnel stationed at the southern Turkish base after the German Parliament voted in June to label as genocide the killings of Armenians by Ottoman Turks a century ago.

Turkey gave the go ahead for Wednesday's visit by the seven-member, cross party delegation after the German government last month stressed that the parliamentary resolution wasn't legally binding.

Germany has reconnaissance and re-fueling aircraft at Incirlik, along with about 250 military personnel.

Some lawmakers said the Incirlik mission couldn't be extended later this year if visits weren't allowed, raising the possibility of a diplomatically delicate withdrawal to another country.