(Adds details, Brotherhood reaction)
CAIRO, July 26 (Reuters) - Egyptian authorities havedetained President Mohamed Mursi for 15 days over an array ofaccusations, including killing soldiers and conspiring with thePalestinian group Hamas, the state news agency said on Friday.
The report came just hours before millions of Egyptians wereexpected to take to the streets in mass rallies for and againstEgypt's first freely elected leader, who was ousted by themilitary on July 3.
Mursi has been held by the military since his downfall, butuntil Friday's step by an investigating judge, he had not facedany formal legal measures. The charges relate to his escape,along with other top Brotherhood leaders, from a prison north ofCairo.
The report on the state news agency said investigating judgeHassan Samir had confronted Mursi with evidence during hisquestioning. It did not say when or where he had beenquestioned.
A spokesman for the Muslim Brotherhood, which says the armyhas staged a coup against the democratically elected head ofstate, described the accusations as "ridiculous". GehadEl-Haddad said they marked the return of the "old regime".
Mursi and many other Brotherhood leaders were rounded up bythe authorities during the 2011 uprising that swept HosniMubarak from power.
The accusations listed against Mursi included arson,destruction of prison records and "collaboration with Hamas toundertake aggressive acts in the country, attacking policefacilities, officers and soldiers".
It also accused him of "killing some prisoners, officers andsoldiers deliberately and with prior intent". It added theaccusation of "kidnapping some officers and soldiers".
The prosecutor has issued a gag order stipulating the mediamay only publish his statements on the case, citing the secrecy of the investigations and "national security. (Reporting by Tom Perry; Writing by Crispian Balmer; Editing byMichael Georgy)