South Portland officials are negotiating to sell the former National Guard armory on Broadway to a Topsham development company.

The City Council discussed the pending sale of the high-profile, often-vacant building during a closed-door session Monday and authorized City Manager Jim Gailey to move forward with negotiations, according to city officials.

The interested buyer is Priority Real Estate Group of Topsham, Gailey said during the public council meeting that followed. More information about the deal will be announced when it’s finalized, possibly as soon as this week, Gailey said.

The council authorized Gailey to market and sell the former armory in June.

Priority Real Estate, headed by Jim Howard, has built, owns or manages more than $100 million in commercial properties, including professional and medical offices, educational facilities, and retail, manufacturing and industrial space, according to the firm’s website.

The company has worked extensively with state and local officials across Maine and specializes in site location, building design, project permitting, construction and budget management and community relations.

The former armory at 682 Broadway has been vacant since Fore River Sound Stage moved out last spring. The city paid $650,000 for the property in 2006 and the building stood empty until Fore River Sound Stage rented it in 2011.

Eric Matheson, the sound-stage operator, had signed a five-year lease, with options for an additional decade. Matheson said he could no longer afford to operate and make necessary renovations without tax incentives. The building has no heat or hot water.

City officials and Matheson terminated the $550-per-month lease by mutual agreement on Jan. 31 and Matheson had to move out by the end of April.