LAS VEGAS — Federal officials have rescinded a $5 billion contract awarded to a firm that had been a subsidiary of defense contractor Lockheed Martin Corp., just days after announcing the company would manage a vast former nuclear proving ground north of Las Vegas.

National Nuclear Security Administration officials declined Friday to provide details about the Department of Energy announcement that it’s renewing the process to award a 10-year contract to operate the Nevada National Security Site.

After declaring Aug. 26 that the contract went to Nevada Site Science Support and Technologies Corp., the government said, it learned the company was no longer a Lockheed Martin subsidiary but had been sold to Virginia-based Leidos Innovations Corp.

The statement said failure to notify the contracting officer about the ownership change raised “substantial questions” about the bid and award.

Leidos spokeswoman Melissa Koskovich said in an email that her firm was disappointed but stands behind its contract proposal and hopes to resolve the issue. She noted the award announcement called the winning bid the “best value to the government.”

Managing the 1,360-square-mile facility has interest from major firms including Bechtel and the current operator, National Security Technologies LLC. That’s a Northrop Grumman joint-venture with three partners.

The award statement had said the Lockheed Martin affiliate was partnering with a subsidiary of engineering and construction company Fluor Corp., and with Las Vegas-based Longenecker & Associates.

Officials with National Securities Technologies declined to comment.

Its contract had been set to expire Sept. 30, but it will continue managing the site until a new manager is picked, the Energy Department said.

As the Nevada Test Site, the area hosted more than 1,000 nuclear detonations from 1951 to 1992. It is now used for experiments and safety training related to the nation’s nuclear stockpile.