A Cairo criminal court accepted on Tuesday an appeal by Egypt's Supreme State Security Prosecution against a previous court order for the release of journalist and researcher Ismail Alexandrani.
The court also ordered that Alexandrani be detained for 45 days.
The prosecution had appealed against a Sunday court order to release Alexandrani, who is being investigated over charges of "joining a terrorist group" and spreading false news.
The investigative journalist, who specialises in Sinai affairs, has remained in detention without trial since his arrest in December 2015, when the prosecution accused him of "spreading false news regarding the situation in Sinai."
Several Egyptian and international rights groups have condemned Alexandrani's arrest and detention.