LONDON — A British toddler who went missing on a Greek island 25 years ago is believed to have been killed in a construction-site accident that was covered up for almost a quarter of a century, police said Monday.

The parents of Ben Needham — who disappeared on the island of Kos on July 24, 1991 — clung for years to the hope that he was still alive.

British police began a new search last month after receiving a tip that Ben might have been killed by a backhoe, whose driver has since died.

Detective Inspector Jon Cousins of South Yorkshire Police said the search had uncovered an item thought to have been with 21-month-old Ben at the time of his disappearance, but no remains have been found.

Cousins said heavy machinery, including a large backhoe, was being used to clear land in the area behind the farmhouse that was being renovated by the Needham family. He said it was his “professional belief” that the boy died in an accident near the house, where he was last seen playing.

Speaking before the announcement, Ben’s mother Kerry Needham said she wanted “to tear up the whole island” to find her son’s remains.

“Someone knows where he is,” she told the Daily Mirror newspaper. “For God’s sake, help me find him. We know he’s dead, but we need to find him.”

Cousins said the police investigation remained open, and “we will not stop in our quest to find further answers for Ben’s family.”