Seven of the 24 runners who won the men's and women's divisions of the London Marathon from 2001 to 2012 recorded suspicious blood scores suggestive of doping, "The Sunday Times" newspaper reported.

The newspaper also reported that one in four winners of major city marathons around the world - in London, Boston, Chicago, New York, Berlin and Tokyo - "had given blood tests that suggest they may have doped to improve their performance over time."

The paper did not name the suspected athletes.

Officials 'concerned'

London Marathon chief executive Nick Bitel said in a statement released Sunday that organizers were "very concerned" by the allegations.

He said he and his staff were doing their best to prevent doping, but were unable "to do it all on our own."

He added that the London Marathon paid for athletes to be tested, but left the testing up to the UK Anti-Doping agency.

The statement also said that the organizers would seek to make athletes who failed doping tests repay the prize money.

The new allegations come after the newspaper and German broadcaster ARD alleged rampant doping in athletics last week, citing leaked test results from an International Association of Athletics Federations database.

The IAAF, the governing body for global athletics, has rejected the claims as being based on "incomplete data."

tj/mkg (AP, AFP)