Ian Rapoport of NFL Network reported the two sides failed to agree despite "intense" negotiations.
Bell, 25, will make $12.1 million as the Steelers' franchise player in 2017. He rushed for 1,268 yards and seven touchdowns last season, adding 75 receptions for 616 yards.
"Unfortunately, we were unable to agree to terms on a long-term contract with Le'Veon Bell prior to today's deadline," general manager Kevin Colbert said in a statement. "Le'Veon is scheduled to play this year under the Exclusive Franchise Tag designation. We will resume our efforts to address his contract situation following the 2017 season."
Bell seemingly responded to the news on Twitter:
The Steelers could franchise Bell again in 2018, which would guarantee him no less than $14.5 million in guaranteed base salary. But given the shelf life of running backs and the potentially exorbitant cap hold Bell could have if franchised again, a long-term deal remains the likeliest option.
For now, the question is when Bell will arrive in camp. He is yet to sign the franchise tender, which means he is not technically under contract. That makes him eligible to skip all team activities up until Week 1 without any financial repercussions from the team.
"I'm good with everything, just taking it day to day for real," Bell told ESPN.com's Jeremy Fowler of his contract situation.
The Steelers could still rescind the franchise tag if Bell holds out deep into camp, but that's a near-nuclear option that would shock the entire league. Bell would instantly garner offers that featured two or perhaps even three times the guarantees he's scheduled to make in 2017 given his age and skill set.
There may be no more consistently productive back in the NFL when healthy. Keeping Bell on the field has been the major issue, as a combination of injuries and off-field problems has caused him to miss 17 games in four seasons.
He is currently recovering from surgery after aggravating a groin injury in the Steelers' AFC Championship Game loss to the New England Patriots.