William J. Baer, assistant attorney general for the antitrust division at the US Justice Department, told the New York Times it would be difficult for any of the country’s top four mobile operators to win regulatory approval for a merger.

Baer’s comments appear to throw cold water on recent speculation that Sprint and T-Mobile US – the third and fourth-largest operators respectively – will soon pool their resources to mount a stronger challenge to Verizon Wireless and AT&T.

Talking to the New York Times, Baer said further consolidation among the top four would face intense scrutiny because consumers have enjoyed “much more favourable competitive conditions” since the anti-trust division blocked a proposed merger between AT&T and T-Mobile in 2011.

“It’s going to be hard for someone to make a persuasive case that reducing four firms to three is actually going to improve competition for the benefit of American consumers,” said Baer, although he did not refer specifically to a potential tie-up between Sprint and T-Mobile US.

He added that any proposed transaction would get a “very hard look” from the antitrust division.