SAN FRANCISCO: Instagram on Thursday became part of Facebook as the social network completed its billion-dollar acquisition of the smartphone photo-sharing service.

“Very excited to announce that we're now officially joining the Facebook family,” Instagram co-founder Kevin Systrom said in a Facebook post tagged as being made using a mobile phone in Japan.

“I'm psyched for the next chapter of this long journey.”

US regulators in August closed an investigation into Facebook's deal to buy the startup behind photo-sharing smartphone application Instagram, taking no action.

The Federal Trade Commission reserved the right to revisit the matter.

The big ticket purchase was seen by some as a move by Facebook to strengthen defenses against Google and blazing hot newcomer Pinterest just ahead of the Facebook public offering.

“For years, we've focused on building the best experience for sharing photos with your friends and family,” Facebook co-founder Mark Zuckerberg said in announcing the deal in April.

“Now, we'll be able to work even more closely with the Instagram team to also offer the best experiences for sharing beautiful mobile photos with people based on your interests.”

Facebook said that it planned to let the San Francisco-based startup grow independently while tapping into Instagram expertise to improve ways for people to share pictures on the social network.

“So many of us at Facebook love using Instagram to share moments with our friends,” Facebook vice president of engineering Mike Schroepfer said in a blog post.

“That's why we're so excited to bring Instagram to Facebook and see what we can create together,” he continued.

“We also can't wait to work with the talented Instagram team to improve the mobile experience.”

Facebook users have increasingly taken to accessing the social network using smartphones or tablet computers.