The U.S. government has agreed to lease six floors of 1 World Trade Center, which ensures that at least half the tower will have paying tenants when it opens in 2014.

The Port Authority of New York and New Jersey and its partner in the project, the Durst Organization, announced the deal Wednesday.

The U.S. General Services Administration will occupy about 270,000 square feet in the tower for two decades.

Other tenants that have signed leases include publisher Conde Nast, which is renting 1.2 million square feet. The Vantone China Center is leasing 190,000 square feet.

Together, those tenants will account for about 55 percent of the space in the tower, which will be among the world's tallest skyscrapers.