Turkey and Germany were working to finalise a memorandum of understanding to agree within a legal framework the deployment of six Tornado reconnaissance aircraft as well as one refuelling aircraft at the Incirlik air base, the source said.
An advance German team was in Turkey last weekend to inspect the base in the southern Adana province in order to make sure that these reconnaissance aircraft can be deployed there, the source added, asking not to be named.
"We need an agreement. Turkey is a sovereign state," the source said.
Since Turkey gave its approval to Washington earlier this year after months of talks, Incirlik has become a key launch-pad for US planes bombing IS-held targets in Syria.
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The German cabinet had yesterday approved a mandate offering military assistance to back the fight against IS which would sharply step up its role in the US-led coalition against the extremists.
The package, which still requires parliamentary approval, covers six Tornado reconnaissance jets, one refuelling aircraft, a naval frigate and up to 1,200 troops following a request from France in the wake of deadly jihadist attacks in Paris last month.
A German frigate is intended to protect the French aircraft carrier Charles de Gaulle in the eastern Mediterranean, from which fighter jets are carrying out bombing runs, and the tanker aircraft could refuel them mid-air to extend their range.