The family of a Malaysian man detained for allegedly insulting a state sultan on Facebook is defending his right to free speech and calling for his release.

Police arrested 27-year-old Ahmad Abdul Jalil in Kuala Lumpur and took him to southern Johor state late Friday.

His sister Anisa Abdul Jalil says the family was told he was being investigated for seditious remarks against the Johor sultan. But she said the family did not know what the offensive postings were. She said Monday the family was worried as Ahmad has been kept incommunicado since his arrest.

Police couldn't be immediately reached for comment.

Under Malaysian law, acts that provoke hatred against royal rulers are considered seditious.