Miami commissioners Thursday approved a controversial plan to allow a developer to erect two skyscraper-size electronic billboards on top of new parking garages next to the Arsht Center.

Commissioner Mark Sarnoff argued the billboards will help jump-start development between downtown and the Omni and money the developer agreed to pay the city will help fund Museum Park downtown.

"I think you have extracted as much blood as you are going to get'' out of the developer, Sarnoff said before the commission's 4-1 vote.

Commissioner Frank Carollo voted against the towers, saying a decision could have waited until September so the city could have done a deeper review.

Developer Mark Siffin proposed building the towers, which would display flashing ads on giant LED screens rising 250 and 350 feet above a 100-foot parking garage -- for a total height of up to 50 stories.

The towers -- which are expected to generate tens of millions of dollars in ad fees -- would sit atop a new multistory parking garage that Siffin proposes to build behind the historic Boulevard Shops on Biscayne Boulevard, across Northeast 14th Street from the Arsht's Knight Concert Hall.

The lots it would occupy are owned by The McClatchy Co., parent of The Miami Herald.

Siffin has said the towers are necessary to finance the garage as well as a long-stalled retail development, City Square, which the commission had approved for adjacent Herald lots.

If the towers are authorized, Siffin pledges to complete the retail project, which he says will revive the blighted area surrounding the Arsht.