BERLIN (Reuters) - Germany has grounded half of its aging Tornado fighter jets, including six currently deployed to Turkey as part of the fight against Islamic State, after discovering loose screws that cannot be properly tightened in some key cockpit equipment.

A spokesman for the Defence Ministry said the issue affected 42 of Germany's 85 Tornados, built by Airbus Defence and Space , including the six jets being used for surveillance flights out of Incirlik air base near the Syrian border.

He said the issue centered on the screws used to fasten the control and display unit in the rear of the jet's cockpit.

He said the aircraft would not be allowed to fly until a solution had been found, since loose screws could cause problems elsewhere in the aircraft.

A spokeswoman for Airbus Defence and Space said the firm had discovered the problem during routine maintenance and reported it to the German authorities. "We are working with the supplier in order to define the root causes and prevent similar occurrences in the future," she said.

It was not immediately clear how long it would take to resolve the issue, or the likely cost.

The issue affects the newer ASST A3 model of the Tornados, which first entered into service between 1981 and 1992.

(Reporting by Andrea Shalal; Editing by Kevin Liffey)