Since its new Leonardo da Vinci exhibition became a blockbuster success, London's National Gallery is facing an unusual problem: having to crack down on the resale of its tickets online.

Gallery officials said Wednesday that they were "very disappointed" at learning that tickets were being resold online — some at significantly inflated prices — and pointed out that reselling tickets is against the venue's terms and conditions.

The National Gallery in London limited the number of visitors for its Leonardo da Vinci exhibition and now, some online resellers are offering tickets at exorbitant prices. Dan Kitwood/Getty Images

"Our website clearly states: 'Tickets that have been resold will be cancelled without refund and admission will be refused to the bearer,'" a gallery spokeswoman told Reuters, adding that staffers will be carefully checking tickets.

The gallery has also been contacting various companies and websites to request an immediate halt to resales.

Leonardo da Vinci: Painter at the Court of Milan, which focuses on his time as a court artist in the 1480s and 1490s, opened Nov. 9 and runs through Feb. 5, 2012.

The show has been described as the most complete display of the artist's few surviving paintings — including a number that have never before been shown publicly — and received rave reviews from critics. Because the gallery limited the number of tickets sold each day, it has sold out.

Though tickets carry a face value of £16 (about $26 Cdn), pairs of tickets were discovered on sale for much more — as high as £600 (about $975 Cdn) — online.