Three months after Sri Lanka was rocked by deadly anti-Muslim riots fuelled by online vitriol, Facebook is training its staff to identify inflammatory content in the country's local languages, AFP reported.

The social network has been seeking penance in Sri Lanka after authorities blocked Facebook in March as incendiary posts by Buddhist hardliners fanned religious violence that left three people dead and reduced hundreds of mosques, homes and businesses to ashes.

Until the week-long ban, appeals to Facebook to act against the contagion of hate speech had been met with deafening silence, at a time when the California-based tech giant was reeling from unprecedented global scrutiny over fake news and user privacy.

"We did make mistakes and we were slow," Facebook spokeswoman Amrit Ahuja told AFP in Colombo.

The dearth of staff fluent in Sinhala - the language spoken by Sri Lanka's largest ethnic group - compounded the issue, with government officials and activists saying the oversight allowed extremist content to flourish undetected on the platform.

Ahuja said Facebook was committed to hiring more Sinhala speakers but declined to say how many were currently employed in Sri Lanka.

"This is the problem we are trying to address with Facebook. They need more Sinhala resources", said the island's telecommunications minister Harin Fernando.

Since the violence broke out in March, two high-level delegations from the company have visited Sri Lanka, where ethnic divisions linger after decades of war, to assure the government of its intent.

Ahuja said Facebook was working with civil society organisations to familiarise its staff with Sinhala slurs and racist epithets.

Complex local nuances have added to the challenge. The word for "brother" in Tamil - also an official language in the country - can be a derogatory term in Sinhala when a slight inflection is used.

Ahuja said Facebook has since taken down "hate figures and organisations" in Sri Lanka including the Bodu Bala Sena, a radical Buddhist outfit that is blamed for attacks against Muslims in recent years.