Egypt's State Prosecution has ordered that eight suspects, who were extradited from Kuwait in July, be detained for 15 days pending investigation.
Prosecutors accuse the suspects of working toward plotting terror operations targeting state institutions, and of membership to an "outlawed terrorist organisation", in an apparent reference to the Muslim Brotherhood which was labelled a terrorist group in 2013 following a military coup that ousted the country's first democratically-elected civilian president who hailed from the organisation.
The men's detention is expected to be repeatedly renewed.
Kuwaiti authorities had said in July that they had arrested a "Muslim Brotherhood cell", whose members were Egyptian nationals who had been on the run in Kuwait and extradited them to their home country in coordination with Egyptian authorities.
At the time, the state news agency KUNA quoted Deputy Foreign Minister Khaled Al-Jarallah as saying that his country's security cooperation with Egypt "is very high. We are satisfied with this cooperation because … we realize the security of Egypt and Kuwait were linked."