WASHINGTON — A US trade regulator has launched an investigation into Facebook’s $1-billion acquisition of photo-sharing site Instagram, which may delay the closing of the deal, the Financial Times reported Thursday.

According to people familiar with the matter, the US Federal Trade Commission (FTC) has launched a probe into the deal that focuses on competition issues. The investigation — expected to take six to 12 months, according to the people — may postpone the acquisition’s closing beyond the second quarter, when the company had targeted wrapping up the deal.

The FTC has already begun collection information from at least two of Facebook’s largest competitors, people familiar with the matter said.

Competition probes are routine for most large acquisitions, but the probe is still cause for concern for the social network, as it puts the final touches on an IPO scheduled for May 18.

Facebook, which announced the deal in April, declined to comment.