Makan Delrahim, the assistant attorney general for antitrust, said that most proposed transactions were either good for consumers or neutral.

But the department's decision in November to sue to stop AT&T Inc, which owns DirecTV, from buying Time Warner Inc made investors question whether other vertical deals might also meet with scepticism from antitrust enforcers.

Delrahim said that was overblown.

"I understand that some journalists and observers have recently expressed concern that the antitrust division no longer believes that vertical mergers can be efficient and beneficial to competition and consumers," he said.

Delrahim said that some of these point at the decision to sue to try to stop AT&T from buying Time Warner "as a supposed bellwether," he said. "Rest assured these concerns are misplaced."

Two other vertical deals under review are Cigna Co plan to buy Express Scripts Holding Co for $52 billion (£38.7 billion) and CVS Health Corp's planned merger with Aetna Inc for $69 billion.

(Reporting by Liana B. Baker; Writing by Diane Bartz; Editing by Lisa Shumaker)

By Liana B. Baker