The riots in early 2018 erupted as anti-Muslim anger was whipped up on social media, forcing the Sri Lankan government to impose a state of emergency and block access to Facebook.
The tech giant commissioned a probe into the part it may have played, and investigators said incendiary content on Facebook may have led to violence against Muslims.
"We deplore the misuse of our platform," Facebook said in a statement to Bloomberg News after the findings were released Tuesday. "We recognize, and apologize for, the very real human rights impacts that resulted."
At least three people were killed and 20 injured in the 2018 unrest, during which mosques and Muslim businesses were burned, mainly in the central part of the Sinhalese Buddhist-majority nation.
The hate speech and rumours spread on Facebook "may have led to 'offline' violence", according to Article One, the human rights consultancy hired to conduct the investigation.
The consultants also suggested that before the unrest, Facebook had failed to take down such content, which "resulted in hate speech and other forms of harassment remaining and even spreading" on the platform.
Article One said one civil society organisation had tried to engage with the company on the misuse of Facebook as far back as 2009.
In 2018, officials had said mobs used Facebook to coordinate attacks, and that the platform had "only two resource persons" to review content in Sinhala, the language of Sri Lanka's ethnic majority whose members were behind the violence.
Facebook has 4.4 million daily active users in Sri Lanka, according to the report by Article One.
The firm said Tuesday it had taken a number of steps in the last two years to better protect human rights.
"In Sri Lanka... we are reducing the distribution of frequently reshared messages, which are often associated with clickbait and misinformation," Facebook said in a statement accompanying reports, which also looked at Indonesia and Cambodia.
Facebook has apologised for its role in the deadly communal unrest that shook Sri Lanka two years ago after an investigation found that hate speech and rumours spread on the
platform may have led to violence against Muslims.
It said it had also hired more staff, including Sinhala speakers, and started using detection technology to protect vulnerable groups.