LONDON — International Olympic officials have opened a high level investigation into allegations that authorized agents in more than 50 countries — including a national Olympic committee — were involved in selling London Olympics tickets on the black market.

The International Olympic Committee convened an emergency session Saturday to discuss a dossier of evidence presented to it by Britain's Sunday Times. The newspaper published an investigation Sunday claiming that officials have been offering tickets for the July 27-Aug. 12 games, including hot events such as the men's 100m final, at vastly inflated prices.

One of the most damaging allegations was against Spyros Capralos, the Greek Olympic Committee president and top organizer for the 2004 Athens Olympics. He was quoted as saying he had "pulled strings" with London organizing chairman Sebastian Coe to obtain an extra batch of premium tickets, on the pretext that demand in Greece outstripped expectations.