Egypt's chief prosecutor has referred 28 people to a criminal court on charges including forming an illegal group aiming to topple the government.

Sunday's statement by prosecutor Nabil Sadek says the suspects face an array of additional charges, including inciting violence and disseminating false news.

The statement says the suspects formed an illegal group, "The Egyptian Council for Change," to incite against the state and its institutions.

It says only nine of the 28 suspects are in custody. No date has been set for the trial. Egypt has intensified a long-running crackdown on dissent since President Abdel-Fattah el-Sissi's re-election in March.

The arrests are part of a wider crackdown on dissent since the 2013 military ouster of an elected Islamist president following mass protests against his one-year divisive rule.