More than 650,000 Rohingya Muslims have fled Myanmar's Rakhine state into Bangladesh.

The UN human rights experts have blamed Facebook for playing a key role in spreading hate speech against the Rohingya Muslims in Myanmar.

Marzuki Darusman, Chairman of the UN Independent International Fact-Finding Mission on Myanmar, said on Monday that the social media platform had played a "determining role" in Myanmar.

"As far as the Myanmar situation is concerned, social media is Facebook, and Facebook is social media," ABC Online quoted Darusman as saying.

More than 650,000 Rohingya Muslims have fled Myanmar's Rakhine state into Bangladesh since insurgent attacks sparked a security crackdown last August.

"(Social media) has ... substantively contributed to the level of acrimony and dissention and conflict, if you will, within the public a Hate speech is certainly of course a part of that," said Darusman.

UN Myanmar investigator Yanghee Lee said that "everything is done through Facebook in Myanmar," adding it has been used to spread hate speech.

"I'm afraid that Facebook has now turned into a beast, and not what it originally intended," she said.

Lee was speaking at the UN's Human Rights Council in Geneva. Facebook did not immediately comment on the fresh charges.

Lee, who was banned from Myanmar last year after it claimed a previous report by her was biased and unfair, said she had seen evidence that Myanmar's military was continuing to target the Rohingya, razing their villages.

Last week, Sri Lanka barred social messaging networks, including Facebook, following violence against Muslims in Kandy district.

The government ordered internet and mobile service providers to temporarily block Facebook, WhatsApp and Instagram, as well as messaging service Viber, after officials said these platforms were fueling online hate speech.