Facebook CEO Mark Zuckerberg gave a full-throated defense of his company's ownership of Instagram on Wednesday, describing the hefty competition that the combined company faces in the market.

Speaking on a call with analysts following Facebook's third-quarter earnings report, Zuckerberg was asked how the increased regulatory scrutiny the company faces will affect its ability to roll out new services in new markets.

Zuckerberg immediately focused his answer on Instagram, the photo-sharing app that Facebook purchased in 2012 for $1 billion and that now has more than 1 billion monthly active users.

"A lot of the antitrust questions that are out there that are going to be about our acquisition of Instagram, right?" Zuckerberg said. "There's going to be a lot of scrutiny of that acquisition in particular."

Democratic presidential candidate Sen. Elizabeth Warren has called for the breakup of Facebook, specifically the divesting of Instagram, a sentiment shared by Facebook co-founder Chris Hughes, who published a New York Times op-ed claiming the deal should be "unwound." Additionally, Facebook is facing investigations and probes from the Federal Trade Commission, the Department of Justice and 47 attorneys general related to antitrust issues.

Zuckerberg began his latest defense by highlighting the competitive environment Facebook was in before the deal took place. At the time, Instagram only had 13 employees supporting the app's 30 million users.

"In some ways we considered Instagram to be a competitor, but we have always thought that the better way to think about Instagram was that it was complementary to Facebook and what we're doing," Zuckerberg told analysts.

He's trying to make the point that whatever market strength Instagram now has is the result of the work that's taken place since Facebook acquired it.