LONDON—Unesco, the cultural agency of the U.N., has warned officials in London and Edinburgh that urgent action must be taken to protect seven world heritage sites — among them the old town of Edinburgh, Stonehenge, and the Georgian center of Bath — in the U.K. that are endangered by building developments, the Guardian reports.

Unesco also said that the country is ignoring its legal obligations to protect the sites in some cases and that the Tower of London may go on the list of endangered world heritage sites if officials do not strengthen their planning guidelines for the area. Unesco worries that the Tower of London and its 13th-century walls will be overshadowed by Renzo Piano's planned London Bridge tower, nicknamed the "shard of glass," and a 39-floor tower on Fenchurch Street.

The organization plans to send two teams of inspectors to Edinburgh and Bath this winter to investigate concerns that new buildings in the cities will damage the sites' "integrity" and "outstanding universal value." The world heritage committee said it "deeply regrets" Edinburgh city council's decision to build a hotel, housing, and office development called Caltongate next to the Royal Mile, despite evidence from experts that the development will ruin the medieval old town's form.

The committee also wrote in the final report from its annual meeting in July in Quebec, which has just been released, that the U.K. may have breached world heritage site guidelines by failing to warn it about Caltongate.

A number of British architects and conservationists have spoken out in support of Unesco's concerns. Marcus Binney, chairman of Save Britain's Heritage, said: "Heritage has taken a back seat to Cool Britannia and encouraging everything modern, and we're now uncomfortably in the limelight for failing to have proper policies to protect our world heritage sites."

Britain's Department for Culture, Media, and Sport said it is introducing a heritage protection bill that will give all sites in the country the same legal protection as conservation areas. The department added that its delegation to the Quebec meeting had successfully challenged some of Unesco's criticisms by demonstrating that its planners were creating new guidelines on protecting a number of sites and their skylines.

"The tone of the meeting was very positive, and our delegates came away with a very positive feeling about the likely final outcome," the department said. "Nothing has been said or received subsequently to alter this impression."

Unesco has asked the U.K. to write detailed progress reports responding to its concerns by February.