Facebook on Thursday boasted of a new achievement with a billion people using the leading social network in a single day. "We just passed an important milestone," chief executive and co-founder Mark Zuckerberg said in a post on his Facebook page. "On Monday, 1 in 7 people on Earth used Facebook to connect with their friends and family."

It was the first time that a billion people used Facebook in a single day, according to Zuckerberg.

"When we talk about our financials, we use average numbers, but this is different," Zuckerberg said.

"This was the first time we reached this milestone, and it's just the beginning of connecting the whole world."

Seperately, Facebook's Instagram has added new layout options in addition to its signature square for pictures and videos in a bid to attract more advertisers and to stop users defecting to more flexible services such as Snapchat.

The move addresses the wishes of many of its 300 million users, who have been constrained by the square format.

One in five photos and videos posted on the service do not fit the square format, Instagram said in a blog post.

"Friends get cut out of group shots, the subject of your video feels cramped and you can’t capture the Golden Gate Bridge from end to end," it said.

From Thursday, Instagram's web-based service and its mobile apps running on Google's Android system and Apple's iOS will allow portrait and landscape formats, giving both users and paying advertisers more options.

The move should attract more advertising revenue for Instagram, which said in June it would open its platform to all advertisers by the end of the year, rather than just to select brands.