TOKYO — The architects behind a scrapped plan for the 2020 Tokyo Olympic stadium blamed the bidding process and rocketing building costs for the spiraling price tag, striking back at claims that it was because of the design.
Zaha Hadid Architects said the contractors were chosen before they submitted cost estimates in a two-stage tender process. The cost rose to $2 billion, nearly double the original estimate, and more expensive than any sports stadium ever built.
‘‘Our warning was not heeded that selecting contractors too early in a heated construction market, and without sufficient competition, would lead to an overly high estimate of the cost of construction,’’ the architects said in a lengthy statement issued from their London office on Tuesday.
The government tossed out the plan 11 days ago amid mounting public criticism of the cost, and said it would start new design and construction competitions.
Two Japanese construction giants, Taisei Corp. and Takenaka Corp., which were part of the earlier plan, are expected to put in another bid. Taisei was to build the stands, and Takenaka would have built the roof, including a pair of giant steel arches.
Construction was due to start in October, and the delay means the new National Stadium will not be available for the Rugby World Cup in 2019, which annoyed World Rugby.
The Japan Sport Council, the body overseeing the project, attributed about one-third of the increase in price to rising labor and materials costs, and two-thirds to the unusual design by Zaha Hadid.
Shota Miyazaki, a spokesman for the overseeing body, said it stands by its conclusion that the surge in the cost estimate was mainly due to the design and rising construction costs.
Zaha Hadid said it learned of the cancellation of the deal through news reports, and received a brief official notification from the Japan Sport Council afterward.
Her office also urged Japan to stick to her design team ‘‘to reduce the risk of further increases in costs, the venue not being ready in time for the Tokyo 2020 Games, and being of lower quality.’’
The architects have also written to Prime Minister Shinzo Abe ‘‘to offer our services to support his review of the project with the current design team,’’ her office said.
Miyazaki confirmed the council canceled the contract on July 17, the day the government announced it publicly, and said there has been no counter-proposal or other offer from the Zaha Hadid office.
The council has already paid $12.9 million to the architects through March 2014, as part of a nearly $49 million contract.