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The alleged disappearance of a pink diamond worth $50 million from a vault is being investigated, Swiss officials said Monday.

The Geneva prosecutor general's office confirmed it launched an probe after South African diamond trader Sylla Moussa filed a complaint alleging his 50.56-carat gem had disappeared.

Moussa told NBC News that he had deposited the diamond with storage company Malca-Amit in a vault at Geneva's airport in 2007. But despite receiving email and verbal confirmation in 2013 that his stone was safe, he said it was not there when he visited in August.

"If I do not find my diamond then I want my $50 million," said Moussa, who runs Johannesburg-based Sylla Diamond International and also has operations in the West African county of Guinea. "I am the only person authorized to take the diamond out of the vault."

The case was first reported by the Swiss public broadcaster Radio Television Suisse on Sunday. It said Malca-Amit's lawyer had denied the allegations and threatened to sue him for libel.

When contacted by NBC News, Malca-Amit's Geneva director Francisco Bautasta declined to comment.

Henri Della Casa, spokesman for the Geneva prosecutor general, confirmed that an investigation had been launched following a complaint from Moussa last year but declined to comment further because it was an active inquiry.

Malca-Amit operates in more than 30 countries and is well known for storing high-value gems and fine art.