The United States Department of Justice is currently working with a group of more than a dozen state attorneys general as it investigates the market power of major technology companies, the department's antitrust chief, Makan Delrahim, said on Tuesday.
Delrahim said at a tech conference that the government is studying previously-approved acquisitions as part of a broad antitrust review that was announced in July and that scrutinises major tech firms with significant market power.
He added that regulators would examine "whether those were nascent competitors that may or may not have been wise to approve".
But Delrahim also said he did not know whether the companies' intent was to purchase those competitors. "I'm not privy to the facts of each of those investigations," he said.
On July 23, the Justice Department said it was opening a broad investigation into whether Amazon.com Inc, Facebook Inc, Alphabet Inc's Google - and potentially Apple Inc - engaged in anti-competitive practices, including concerns raised about "search, social media, and some retail services online".
More than a dozen states are expected to announce in the coming weeks that they are launching a formal probe, a person briefed on the matter told the Reuters news agency.
"I think it's safe to say more than a dozen or so state attorneys general have expressed an interest in the subject matter," Delrahim said.
In July, eight state attorneys general met with US Attorney General William Barr to discuss the effect of big tech companies on competition, and various antitrust actions.
The New York State Attorney General's office said on Monday that it is continuing to "engage in bipartisan conversations about the unchecked power of large tech companies".
North Carolina Attorney General Josh Stein is also "participating in bipartisan conversations about this issue", his office said.
The department is looking not only at price effects, but also innovation and quality. Its broad antitrust review would next be seeking documents, and could include some compulsory requests, Delrahim said.
After the July announcement, the companies under investigation "immediately reached out to work with us in a cooperative manner to provide information that we need as far as the investigation", Delrahim added.
The Federal Trade Commission (FTC) in June told Facebook it had opened an antitrust investigation. Last month, the FTC resolved a separate privacy probe into Facebook's practices after the company agreed to pay a $5bn penalty. Amazon has also faced an inquiry by the FTC.