Egyptian authorities have detained former president Mohammed Mursi for 15 days over an array of accusations.

The accusations include killing soldiers and conspiring with the Palestinian group Hamas.

The report came just hours before a number of rallies in support of the former president.

Mr Mursi has been held by the military since his overthrow, but until this latest step by an investigating judge, he had not faced any formal legal measures.

The charges relate to his escape, along with other top Brotherhood leaders, from a prison north of Cairo.

The report on the state news agency said investigating judge Hassan Samir had confronted Mr Mursi with evidence during his questioning. 

It did not say when or where he had been questioned.

A spokesman for the Muslim Brotherhood Gehad El-Haddad, which said the army has staged a coup against the democratically elected head of state, described the accusations as "ridiculous".

Mr El-Haddad said they marked the return of the "old regime".

Mr Mursi and many other Muslim Brotherhood leaders were rounded up by the authorities during the 2011 uprising that swept Hosni Mubarak from power.

The accusations listed against Mr Mursi included arson, destruction of prison records and "collaboration with Hamas to undertake aggressive acts in the country, attacking police facilities, officers and soldiers".

It also accused him of "killing some prisoners, officers and soldiers deliberately and with prior intent".

It added the accusation of "kidnapping some officers and soldiers".

The prosecutor has issued a gag order stipulating the media may only publish his statements on the case, citing the secrecy of the investigations and national security.