LONDON — Parts of seat cushions believed to be from the small plane carrying the Argentine soccer player Emiliano Sala and his pilot that disappeared over the English Channel have been found on a French beach, the British authorities said on Wednesday.

The cushions were discovered by the French authorities on Monday near Surtainville, a coastal area in northwestern France, Britain’s Air Accidents Investigation Branch said in a statement.

British investigators have identified a search area of approximately four square miles based on the plane’s path and last known radar position. A specialist vessel will search the seabed for the wreckage at the end of this week, weather permitting, the statement added.

“We are aware that a privately operated search is also being conducted in the area, and we are liaising closely with those involved to maximize the chance of locating any wreckage and ensure a safe search operation,” the statement said.