The San Diego Chargers deceived their fans and the city by working on a stadium plan in the Los Angeles area with the Oakland Raiders, San Diego mayor Kevin Faulconer said Friday.

“The Chargers weren’t being up front with San Diegans, they weren’t being up front with their fans. … That’s not how you get things done,” Faulconer said.

“We deserve an honest dialogue. What we saw speaks volumes about the true intentions and about what’s been happening over the last few weeks.”

Two longtime rivals, the Chargers and Raiders announced in a joint statement Thursday night that they are teaming up to propose a shared stadium in Carson, Calif., near Los Angeles. The Carson site would have a capacity of 68,000 to 72,000, according to the Los Angeles Times.

The teams continue to seek publicly funded stadiums in their current cities, but as a backup plan, they are considering building a $1.7 billion, privately funded stadium in Carson.

The Chargers have criticized the mayor’s stadium task force since Faulconer announced its creation last month.

“It’s now abundantly clear that while we have been working here in San Diego to create a plan for a new stadium, the Chargers have for some time been making their own plans for moving to Los Angeles,” Faulconer said. “This would amount to abandoning generations of loyal Chargers fans.

“I’m more committed than ever to get this done. San Diegans deserve for the team to stay here.”

A more hopeful response followed in Oakland, according to the Los Angeles Times.

Oakland mayor Libby Schaaf said Raiders president Marc Badain assured her Thursday that the team’s “No. 1 priority” is to build a new stadium in the city. Schaaf, who doesn’t believe Oakland should subsidize a stadium, “respects” the Raiders’ need to explore other options for a new home.

“They have done it before and they will do it again,” she said.

A joint statement released by the Chargers and Raiders on Thursday night read, in part:

“We are pursuing this stadium option in Carson for one straightforward reason: If we cannot find a permanent solution in our home markets, we have no alternative but to preserve other options to guarantee the future economic viability of our franchises.

“In short, for the remainder of 2015, we intend to move down two tracks simultaneously: On track one, we will continue to work in our home markets to find permanent stadium solutions that are publicly acceptable. On track two, we will work in Carson to preserve our options, and the future economic viability of our franchises, in the event that our efforts in our local markets fail.

“Throughout this process we will respect the rules and procedures set forth by the league and defer completely to the ultimate decision of the NFL’s owners.”

The Los Angeles area last had an NFL team in the 1994 season, after which the Rams moved to St. Louis and the Raiders moved back to their original home in Oakland.

In January, St. Louis Rams owner Stan Kroenke announced that he planned to build an 80,000-seat stadium in Inglewood, Calif., at the former Hollywood Park site.