Developers of applications for mobile devices should make important disclosures easy for users to find rather than burying them, the Federal Trade Commission said in guidance for technology companies on Wednesday.

The commission, which enforces laws requiring advertising to be truthful and fair, warned in a short video that key disclosures about privacy and other matters should not be buried in long, hard-to-read legal documents.

"If you make objective claims about your app you need solid proof to back them up before you start distributing it," said Laura Berger, an FTC attorney who narrated the video.

Both Google's Android and Apple's app stores have hundreds of thousands of apps available for download.

If advertising appears on an app for Twitter, Facebook or some other social media on a smartphone, necessary disclosures need to be placed close enough to the ad, or prominently enough, to ensure users see it, the FTC said.

Given the limited space available on smartphone screens, that could be difficult, said one person familiar with the industry who asked not to be named for business reasons.

"How can you get disclosures out in the new medium?" he asked. "Without a hyperlink or some other way to signal (a disclosure), you cannot get it onto a screen."

In guidance for online platforms issued on Tuesday, the FTC had urged advertisers to avoid putting promotional messages on mobile and social media platforms like Twitter if the ads required disclosures.

The FTC also discouraged the use of pop-ups for disclosures since they are so often blocked by users.

(Reporting By Diane Bartz; Editing by Tim Dobbyn)