Frontier Airlines on Wednesday said that it offered to buy Spirit Airlines three years after the failure of a previous proposed deal. Frontier valued its stock and cash offer at more than $2.1 billion, far less than the $2.9 billion deal that the airlines had announced in early 2022.

But Spirit said it had rejected the offer for being too low, though it signaled that it would be open to negotiations with Frontier.

Spirit abandoned the earlier agreement in favor of a counteroffer from JetBlue Airways, which was eventually blocked in court by the Justice Department last year. After a string of setbacks, including a failure to renegotiate its debt, Spirit filed for bankruptcy in November.

“As a combined airline, we would be positioned to offer more options and deeper savings, as well as an enhanced travel experience with more reliable service,” Barry Biffle, Frontier’s chief executive, said in a statement.

Frontier first made the offer to Spirit and its creditors on Jan. 7. It revealed that bid publicly on Wednesday, a day after Spirit rejected it. In a securities filing, Spirit said it had told Frontier on Tuesday that it would stick with its plan to restructure its finances in bankruptcy court, but remains open to future offers.

Spirit’s chief executive, Ted Christie, and chairman, Mac Gardner, said in a letter to Frontier executives that the latest offer was too low. They also said there was substantial risk associated with the deal, and that Spirit’s creditors were unwilling to invest $350 million as requested by Frontier.

In the letter, the two said that Spirit sees the logic in such a deal, but the current offer was “both inadequate and unactionable.”

This is a developing story. Check back for updates.