Facebook needs to narrow its "sweeping" definition of terrorism to stop governments arbitrarily blocking legitimate opposition groups and dissenting voices, a U.N. Human Rights Council independent expert said in a statement on Monday.

"The use of overly broad and imprecise definitions as the basis for regulating access to and the use of Facebook's platform may lead to discriminatory implementation, over-censoring and arbitrary denial of access to and use of Facebook's services," said Fionnuala Ní Aoláin, U.N. special rapporteur on protecting rights while countering terrorism.