Sandberg was in a New Delhi meeting with small businesses that use Facebook to advertise when she made the apology.
She said: "This was part of ongoing research companies do to test different products, and that was what it was; it was poorly communicated. And for that communication we apologise. We never meant to upset you."
There was uproar among social media users at the weekend when it first emerged that Facebook had carried out a one-week experiment in which the company’s data scientists used an algorithm to determine whether lowering the number of positive or negative posts in users’ news feeds could prompt them to post more positive or negative content.
The experiment was revealed in a scientific paper published in Proceedings of the National Academy of Sciences, prompting anger from experts and users.
It is the first time Facebook has commented on the issue.
Sandberg added: "We take privacy and security at Facebook really seriously because that is something that allows people to share."