A competition probe into Facebook’s $1bn acquisition of photo-sharing service Instagram threatens to postpone the closure of the deal beyond the second quarter, the target set by the company in its initial public offering documents.

The Federal Trade Commission has launched the investigation, according to two people familiar with the matter, and has already begun collecting information from at least one of the social network’s largest rivals. The process could also further slow Facebook’s already lagging mobile strategy.

The competition probe – routine for any deal over $66m – is likely to take six to 12 months, according to several experts. But Facebook said in its IPO documents last month that it expected the deal to close in the second quarter. “That’s terrifically optimistic,” said David Balto, a former policy director at the FTC who now works as an antitrust lawyer.