He stated this in a Q+A session held at Facebook's headquarters in Menlo Park,California.

He said the button would be a way for people to express empathy and Facebook was "very close" to having it ready for user testing.

The "Dislike" button was a constant request of some users after the introduction of the "like" button in 2009.

"Probably many users asked about this, and today is a special day because today is the day that I actually get to say we are working on it, and are very close to shipping a test of it.", said Zuckerberg.

Prof Andrea Forte, an expert in social and participatory media at Drexel University in Philadelphia said, "she suspected that would mainly be used to express mild disapproval, or to express solidarity when someone posts about a negative event like a death or a loss.