In a multi-billion-euro deal with Lockheed Martin, the Belgian government said it would buy 34 radar-evading F-35s to replace its ageing US-made F-16s, from 2023.

Critics called the decision "very bad news" for a more autonomous EU defence strategy, which got a boost after Brexit and US President Donald Trump's election.

Lockheed Martin said it looked forward to ties with "the Belgian government and industry for decades to come," according to a statement on its Twitter feed.

Belgian Prime Minsiter Charles Michel sought to head off his critics when he said Belgium was looking to both Europe and the United States to meet its defence needs.

Belgium is also buying drones, frigates, minesweepers and armoured vehicles "within the framework of NATO and European defence," Michel told a news conference.

"The planes and drones are American, the other equipment is European and Belgium will enjoy the economic benefits," Michel added,

Foreign Minister Didier Reynders said the US offer "was the best from the price and operational standpoint."

The F-35 ran against a bid from the Eurofighter, developed by a European consortium that also comprises Italy's Finmeccanica and Airbus.

Jean-Dominique Giuliani, who heads the Robert Schuman Foundation, a European think-tank, lamented the decision.

"It's not a European choice. It's worse than a slap, it is dreadful for European defence," Giuliani told AFP. "It is very bad news."

The F-35 requires a whole maintenance and operational system that depends "on the control of the United States," he added.

- "Muddy the waters" -

Marking a move away from Europe's decades-long reliance on the United States for its defence, Brussels last year launched "permanent structured cooperation on defence", known as PESCO.

The aim was to unify European defence thinking and to rationalise a fragmented approach to buying and developing military equipment.

France was also likely to be unhappy with the decision.

The United States, acting on behalf of the F-35, and Britain, pushing for the Eurofighter, responded formally to the bidding process Belgium launched in March 2017.

However, the French government took a different tack in September last year by proposing "in-depth cooperation" with the Belgian air force in additon to supplying Rafale fighters, built by the French firm Dassault.

Defence Minister Steven Vandeput said France had ruled itself out with its approach.

"We regret that France voluntarily withdrew from its obligation to present a bid in the framework of our transparent competitive process," he said.

Christophe Wasinski, professor of international relations at ULB University in Brussels, said the announcement of plans to buy 400 French armoured vehicles amounted to government spin.

"It sought to muddy the waters by saying it would buy not just American materiel when the star of these purchases is in fact the F-35," Wasinksi said.

According to Pentagon figures earlier this month, 320 F-35s have been delivered globally, mainly to the US but also to Israel and Britain.