The aircraft carrier lost the F-35B plane last Wednesday. The pilots ejected safely.

There were concerns in NATO that Russia might attempt to get to the sunken wreck of the plane first and be able to glean insights into its cutting-edge technology.

"We'll get it first, I promise you," said Brigadier General Simon Doran, the top-ranking US officer on board.

"We're not concerned at all about recovering it," NATO's Deputy Supreme Allied Commander Europe, General Tim Radford, told journalists on board the vessel in the Mediterranean.

"We're not worried because we are working through the issue at the moment. There was obviously a concern when the plane went down. The pilot is safe which is the most important thing."

He and other officials declined to give any further details about the salvage effort.

The commander of the nine-vessel allied strike group being led by HMS Queen Elizabeth, Commodore Steve Moorhouse, called the loss of the F-35B "a hugely unfortunate incident" and "a setback"

But he said: "The reliability of the aircraft or confidence in it and the project is undiminished."

Britain has so far taken delivery of 21 of the US-made F-35Bs, mostly for its two modern aircraft carriers, HMS Queen Elizabeth and HMS Prince of Wales.

The F-35Bs are designed for short take-off and vertical landing, and are a variant from other F-35s. They are 5th-generation war planes able to be equipped for a range of different missions.