NEW YORK — Spirit Airlines, the target of a budget airline bidding war, said today that it been in talks with JetBlue about last week’s buyout offer while remaining engaged with Frontier Airlines, with which Spirit has already signed a merger agreement.

Spirit said that it has given JetBlue and Spirit the same access to its information and that the Spirit board expects to complete its due diligence on the two offers and have an update for shareholders before they vote on which deal to take at the June 30 special meeting.

JetBlue has offered more in cash than Colorado-based Frontier’s stock and cash bid, but Spirit’s board has rebuffed JetBlue, saying that any such tie-up would face a greater likelihood of being shot down by federal antitrust regulators because of JetBlue’s alliance with American Airlines in the Northeast.

The bidding war for Miramar, Fla.-based Spirit has heated up in the past month, with JetBlue attempting to allay concerns that the U.S. would block its acquisition.

The New York airline last week offered a $350 million reverse break-up fee payable to Spirit if a deal between the two isn’t completed for antitrust reasons, topping its previous contingency plan by $150 million.

Last month, JetBlue went hostile in its attempt to buy Spirit, taking its offer directly to shareholders of the airline. Spirit CEO Ted Christie has said that JetBlue is more interested in breaking up a deal with Frontier than it is in owning Spirit.

Both JetBlue and Frontier say growing by acquiring Spirit would help them compete against the nation’s four dominant airlines: American, Delta, United and Southwest.