The NBA received an official offer Friday from 24 Hour Fitness founder Mark Mastrov and billionaire Ron Burkle to buy the Sacramento Kings and keep the team from moving to Seattle, league spokesman Tim Frank said. No financial details of the proposal have been released.

Sacramento Mayor Kevin Johnson announced the Mastrov-Burkle bid during his State of the City address Thursday night, calling it a “competitive offer.” Johnson tweeted Friday: “The proposal is IN!! A proud day for Sacramento!!”

The Associated Press has reported since Jan. 22 that Mastrov and Burkle were working on a plan to keep the Kings from relocating to Seattle.

Johnson finally announced the proposal publicly on the eve of his self-imposed March 1 deadline. With the league confirming the prospective Sacramento buyers, the only major announcement left is the future owners — and location — of the franchise.

The NBA Board of Governors is expected to vote by mid-April on the Seattle bid. If the league blocks the deal, the Maloofs would still have to agree to sell the team to any potential buyers.

The choice appears to be a tough one for owners. About the only certainty in the seemingly never-ending Sacramento saga came in NBA Commissioner David Stern’s statements during All-Star weekend in Houston.

“I don’t see any scenario where both cities are happy,” Stern said.

Mastrov, among the final bidders for the Golden State Warriors before Joe Lacob and Peter Guber bought the team for an NBA-record $450 million in 2010, is hoping to become the majority owner of the Kings. Burkle, co-owner of the NHL’s Pittsburgh Penguins, will lead the effort to build a new downtown arena that he hopes will lure back a WNBA franchise.

A Seattle group led by hedge-fund manager Chris Hansen and Microsoft Chief Executive Steve Ballmer has had a signed agreement since January to acquire a 65 percent stake in the team for $341 million from the Maloof family. The group already has petitioned the league to relocate the team to Seattle for next season, restore the SuperSonics name and play in KeyArena for at least two years while a new downtown arena is constructed.

Sacramento is hoping to revitalize the city with an arena at the Downtown Plaza shopping mall owned by JMA Ventures, whose officers have said they are eager to participate. To show Sacramento support for the Kings, Johnson also lined up at least 20 local investors who each committed $1 million.

The local group hopes to buy a 7 percent share of the team now under control of a federal bankruptcy court. One of those investors is former Sacramento Kings standout Mitch Richmond.

The mayor also said Sacramento businesses have committed $50 million in sponsorship and season-ticket sales for the Kings over the next five years, which he hopes will be enough to convince NBA owners of the market’s viability.

Seattle hoops fans, meanwhile, have been reeling since owner Clay Bennett — now the chair of the NBA relocation committee — moved the Sonics to Oklahoma City in 2008.

Hansen has been at the forefront of bringing the NBA back to the basketball-loving Pacific Northwest city. He reached agreement with local governments in Seattle last October on plans to build a $490 million NBA/NHL arena near the city’s other stadiums, CenturyLink Field and Safeco Field.

No construction will begin on that project until all environmental reviews are completed and a team has been secured.