The announcement came despite a petition containing more than 100,000 signatures, which allows any matter to go to a vote under Switzerland's direct democracy system.

Although the left-leaning "Stop-F-35" alliance delivered the petition last week, the government said there would not be enough time to hold a vote before US manufacturer Lockheed Martin's offer for 36 F35-As expired.

"A delay in the acquisition of the F-35A would have serious consequences for Switzerland's security," said a government statement.

The Stop F-35 coalition denounced what it called a "cowardly avoidance manoeuvre" and a "mockery of a functioning democracy", demanding a vote before the deal was done.

Switzerland's current air defence set-up will reach the end of its service life in 2030. It began seeking replacements for its ageing fleet of fighter jets more than a decade ago.

The government won a razor-thin referendum in September 2020 backing the military to spend six billion Swiss francs ($6.2 billion) on a new fleet.

The F-35A combat aircraft -- already used by the US Air Force and several European countries -- was chosen ahead of several European rivals.

Two Swiss parliamentary committees launched an investigation into why the model won despite a series of technical problems reported in the United States. They also questioned their high cost.

The Stop-F-35 alliance was formed to try to force the issue to a fresh vote, this time on the choice of F-35As.

But the government said Wednesday that a referendum effectively blocking the purchase deal would set a bad precedent.

Landlocked Switzerland has a tradition of armed neutrality, with mandatory conscription for men.

rjm/apo/jj

LOCKHEED MARTIN