MENLO PARK, Calif. (AP) — What's the worst insult you can throw at a fast-moving company like Facebook? Call its iPhone app slow and poky.

On Thursday, Facebook Inc. addressed users who had gripes with its app for iPhones and iPads with the launch of a faster version. Rather than add a slew of new features, the company said it rebuilt the application from scratch to make it speedier and less clunky.

In a recent demonstration at the company's Menlo Park, Calif., headquarters, the new iPhone app opened about twice as fast as the older version. Photos and comments also load faster. Users can now "like" comments on photos, which wasn't possible with the previous mobile app.

Mick Johnson, mobile product manager at Facebook, said programmers removed some lesser-used features, such as a way to view the app horizontally, to help speed it up.

The mobile arena presents Facebook with its biggest challenge —and its biggest opportunity. That's where its user base is growing the most. At the end of June, Facebook had 543 million users who accessed it with a phone or tablet computer, up 67 percent from 325 million a year earlier. Its overall user base grew 29 percent over the same time period, to 955 million.

But while Facebook ads are well-established on its website, the company only recently started experimenting with mobile advertisements. That's been a concern for investors, who've sent Facebook's stock down by nearly half since the company's initial public offering three months ago.

The iPad version of the new app now features Timeline, the latest version of the profile page that Facebook is rolling out to all of its users.

The app is available for free from Apple's App Store.

Still absent from Facebook's app is any integration of Instagram. That's because Facebook hasn't closed the acquisition of the photo-sharing app. Thought it got a step closer Wednesday, when the Federal Trade Commission said it has closed its investigation into Facebook's planned acquisition.

The FTC said it is not taking action on the deal, which can now go forward as planned. Facebook has agreed to buy Instagram in a cash and stock deal worth about $748 million, based on Facebook's stock price on Thursday. The price tag had been about $1 billion when the companies initiated the deal before Facebook's IPO, in April.