"A group of 25 officers from the police Criminal Investigation Department sealed the offices and nine employee were arrested," the media organisations said in a joint statement. "We condemn this deadly assault on media freedom."
Both news websites linked to the opposition did not update their reports after the raid.
Sri Lanka already facing international censure over its human rights record and a string of unsolved murders of journalists and attacks against the independent media.
Some 17 journalists and media employees have been killed in Sri Lanka in the past decade, pro-opposition websites have been blocked and media organisations opposing government views have been attacked, according to rights groups, the report said.The Island newspaper quoted opposition legislator Mangala Samaraweera as saying that the house of Ruwan Ferdinandez, the editor of Lanka Mirror has also been raided by police.
