A campaign worker for then-presidential candidate Abdel-Monaem Abul Fetouh walks in front of his poster at his headquarters in Cairo, Egypt, in 2012. File picture: Manu Brabo/AP

Cairo - An Egyptian court has sentenced 21 people to death and seven others to up to life in prison on terrorism-related charges.

Thursday's verdict, reported by the state-run MENA news agency, can be appealed.

Out of the 28 on trial, only 12 are in custody while the others - 16 suspects - are at large.

Earlier on Thursday, six suspected members of the now-outlawed Muslim Brotherhood group were ordered detained for 15 days, pending investigation over joining a "terrorist" group.

The six were arrested on Wednesday night on a farm allegedly belonging to detained former presidential candidate, Abdel-Monaem Abul Fetouh, who was also formerly a Brotherhood member.

Egypt has been carrying out a wide-ranging crackdown on dissent since the 2013 military overthrow of Islamist President Mohammed Morsi, a senior Brotherhood figure.