Facebook said Tuesday its ranks of monthly active users had hit the two billion mark -- meaning more than a quarter of the world's population is on the giant social network.

"As of this morning, the Facebook community is now officially 2 billion people!" co-founder and chief executive Mark Zuckerberg wrote in a post on his Facebook page marking the milestone.

"We're making progress connecting the world, and now let's bring the world closer together," he wrote. "It's an honor to be on this journey with you."

Naomi Gleit, a vice president at the internet giant, credited millions of small communities at Facebook for helping drive growth.

"There are two billion people connecting and building communities on Facebook every month," she said. 

More than a billion people take part in "groups" at Facebook each month and more than 800 million people "like" something at the social network on an average day, she added.

Founded in 2004, the social media behemoth hit the billion-user mark five years ago.

- TV shows -

As it has grown, Facebook has consistently updated features to fend off challengers such as Snapchat and adapt to trends such as the migration of news and streaming video online.

In the latest move to deepen its reach, Facebook revealed Monday it is starting production on high-quality television series and gaming shows to be broadcast on its platform.

Working with a small group of partners, Facebook hopes to start putting out episodes of its forthcoming series by the end of the summer, Nick Grudin, the vice president for media partnerships, told AFP.

"Our goal is to make Facebook a place where people can come together around video," Grudin said, noting that Facebook and its collaborators would "experiment with the kinds of shows you can build a community around -- from sports to comedy to reality to gaming."

Facebook's initiative follows similar moves by Netflix, Amazon and the online television platform Hulu -- a joint venture by Disney, Comcast, 21st Century and Time Warner -- who have thrown themselves into content production, as have YouTube and Apple, although on a more modest scale.

- Battling hate -

Chief among the challenges it faces -- along with other social media giants -- Facebook is under pressure to tackle the proliferation of hate speech and extremist content, trolls and misinformation, while safeguarding freedom of speech.

Facebook, Microsoft, Twitter and YouTube announced Monday the launch of an anti-terror partnership aimed at thwarting the spread of extremist content online.

The "Global Internet Forum to Counter Terrorism" intends to share engineering, research and knowledge to help "continue to make our hosted consumer services hostile to terrorists and violent extremists," the companies said.

Each of the technology giants has been working individually to prevent its platforms or services from being used to promote or spread extremist views.

"We believe that by working together, sharing the best technological and operational elements of our individual efforts, we can have a greater impact on the threat of terrorist content online," said a joint statement.

Facebook this month launched a series of counterterrorism measures in the wake of attacks in Manchester and London.