Photo by Steve Adams | Banker & Tradesman Staff / File

Approximately 10 grave sites containing skeletal remains were discovered at a Medford Square property that the city is preparing to sell for a multifamily housing project.

Work was halted at the site behind Medford City Hall this week after an archeological consultant unearthed the grave sites, Mayor Breanna Lungo-Koehn said. The city halted further work and notified state officials.

“We need to create a plan and make sure the entire site should be handled properly, and we’re going to have to follow Massachusetts Historical Commission guidelines,” Lungo-Koehn said.

At least 10 skeletal remains were found in the first trench dug by an archeologist hired by the city as it prepares to sell the property for a potential housing development.

The property includes portions of the former Cross Street Cemetery, which lay in the path of Interstate 93 and was removed in the 1950s. Many of the grave sites and remains were relocated to Oak Grove Cemetery in 1958.

But Medford Historical Commission members suspected that some remains from the Cross Street Cemetery might have been overlooked, and the city hired the archaeologist as part of its due diligence, Lungo-Koehn said.

The delays to the development, and additional costs, are yet to be determined.

“We haven’t even interviewed the applicants yet, so we can be upfront and figure out a plan on who’s going to pay for it,” Lungo-Koehn said.

Last fall, the city issued a request for proposals from developers to build housing on the 3.5-acre site, located between city hall and the Hyatt Place Medford Boston hotel. The site contains approximately 300 parking spaces.

Two developers responded to the offering in December. Details of the proposals have not yet been released.