The U.S. Justice Department is leaning toward rejecting the pending merger between T-Mobile US Inc. and Sprint Corp., Bloomberg News reported, citing a source familiar with the review.

The concessions offered by the wireless carriers are reportedly not enough to satisfy the department's antitrust concerns. Proposed remedies include asset sales, a divestment of Sprint's prepaid brand Boost Mobile and a commitment to a three-year buildout of 5G networks.

In April, Makan Delrahim, head of the Justice Department's antitrust division, said that while 5G may be a deal "efficiency" that can be considered as part of the review, it must be merger-specific and verifiable.

Blocking the deal would mark a rare break between the Justice Department and the Federal Communications Commission, as the agencies normally come to the same decision in merger reviews.

FCC Chairman Ajit Pai earlier said he is ready to recommend the approval of the T-Mobile/Sprint deal, saying that the transaction "is in the public interest." It comes despite FCC Commissioner Jessica Rosenworcel still having "serious doubts" about the merger.

The deal will also need to be approved by a number of states. State attorneys general have raised anti-consumer concerns, warning that they may sue to block the transaction even if the DOJ approves it, according to Bloomberg News.

T-Mobile and Sprint agreed in April 2018 to merge via a stock transaction. At the time, the deal represented a total implied enterprise value of $146 billion.