GENEVA, Feb. 2 (Xinhua) -- The Swiss Air Force has found cracks in a further three of its 30 F/A-18 Hornet fighter jets and they have been taken out of action, the country's Defense Ministry said Friday.

A broken hinge was first discovered on a landing flap of an F/A-18C during an intermediate inspection at the end of January, the Swiss News Agency SDA reported.

It was then decided to submit all remaining F/A-18 jets to tests, to ensure their airworthiness and safety.

Cracks have been found on the landing flaps of three further aircraft, a statement said, and they are now grounded and are being submitted to further analysis.

It is not possible to say whether the parts will be replaced, the estimated cost or when the jets might fly again, the government statement said.

The cracks were not visible to the naked eye but were discovered using a special device.

In all, 23 aircraft underwent tests at military airfields.

Seven are undergoing maintenance at Ruag Aviation, a support company, and are being inspected, the ministry explained.

The U.S.-built F/A-18-Hornet fighter jets have been used in Switzerland since 1997.

The government would like to spend 8 billion Swiss francs (8.6 billion U.S. dollars) on new fighter jets and missile defenses for the Swiss military. The 30 F/A-18s can be used, for example, until 2030.

In 2014 voters rejected spending 3.1 billion Swiss francs on 22 Swedish-built Gripen fighters. It is not clear whether voters will have the final say on this latest 8 billion Swiss franc project.