* Fears of violence as rival camps mobilise for rallies
* Interim PM cites fear of casualties
* Brotherhood says aims for biggest protest yet (Adds statement by Brotherhood leader, ex-PM initiative)
By Tom Perry and Maggie Fick
CAIRO, July 25 (Reuters) - Supporters of Egypt's deposedpresident and his opponents predicted blood on the streets aheadof what could be a violent day of mass protests, summoned by theMuslim Brotherhood and the army in a struggle for the country'sfuture.
In a dramatic escalation of rhetoric ahead of a day thatboth sides view as a potential turning point in Egypt's history,ousted leader Mohammed Mursi's Muslim Brotherhood accused thearmy of pushing the nation towards civil war and committing acrime worse than destroying Islam's holiest site.
The main anti-Mursi youth protest group replied that itssupporters were taking to the streets to "cleanse Egypt".
Army chief General Abdel Fattah al-Sisi, who overthrew thecountry's first elected leader on July 3, has called onEgyptians to take to the streets on Friday to show their supportfor action against "violence and terrorism".
Mursi's Brotherhood, organising its own marches on Fridayagainst Sisi, fears the army appeal is a harbinger of acrackdown to wipe out an Islamist movement that has won repeatedelections since the fall of autocrat Hosni Mubarak in 2011.
Prime Minister Hazem el-Beblawi, head of the interimcabinet, said there was escalating violence by increasinglywell-armed protesters, citing a bomb attack on a police station.
"The presence of weapons, intimidation, fear - this causesconcern, especially when there are calls for many to come outtomorrow from different sides," he told a news conference.
After a month in which close to 200 people have died inviolence triggered by Mursi's downfall, many fear the protestswill lead to more bloodshed.
One security official forecast violence beginning Fridaynight and stretching into Saturday.
"The history of Egypt will be written on those days," saidthe official, part of a security establishment that accuses theIslamists of turning to violence.
Reiterating his group's commitment to peaceful protest,senior Brotherhood politician Farid Ismail accused the securityservices of readying militias to attack Mursi supporters, addingthat Sisi aimed to drag Egypt into civil war.
"His definition of terrorism is anyone who disagrees withhim," Ismail told Reuters. "We are moving forward in completepeacefulness, going forward to confront this coup."
Muslim Brotherhood leader Mohamed Badie issued a statementaccusing Sisi of committing a crime worse than destroying theKabaa - the site in Mecca to which all Muslims face when theypray - "brick by brick".
But many Egyptians are no less passionately backing thearmy, determined to see the Brotherhood reined in.
"There are men carrying guns on the street ... We will notlet extremists ruin our revolution," said Mohammed Abdul Aziz, aspokesman for Tamarud, an anti-Mursi petition campaign thatmobilised protests against his rule.
"Tomorrow we will cleanse Egypt," he told Reuters.
UNCOMPROMISING
Sisi's speech on Wednesday pointed to the deepeningconfrontation between the Brotherhood and the militaryestablishment, which has reasserted its role at the heart ofgovernment even as it says it aims to steer clear of politics.
Saying it moved against Mursi in response to the biggestpopular protests in Egypt's history, the army installed aninterim cabinet that plans to hold parliamentary elections inabout six months, to be followed by a presidential vote.
The Brotherhood, whose supporters have been camped out in aCairo suburb for a month, says it wants nothing to do with thetransition plan. With Mursi still in military detention at anundisclosed location, there is slim hope for compromise.
The country remains deeply split over what happened on July3. The Brotherhood accuses the army of ejecting a democraticallyelected leader in a long-planned coup, while its opponents saythe army responded to the will of the people.
Sisi announced the nationwide rallies after a bomb attack ona police station in Mansoura, a city north of Cairo in which apoliceman was killed. The government said it was a terroristattack. The Brotherhood also condemned the bombing, accusing theestablishment of seeking to frame it to justify a crackdown.
Since Mursi was deposed, hardline Islamist groups have alsoescalated a violent campaign against the state in the lawlessSinai Peninsula, with daily attacks on the police and army.
The army says Sisi's speech did not represent a threat toany party, reiterating the military's backing for nationalreconciliation. The army spokesman said any violence at theforthcoming rallies would be dealt with decisively.
At the Brotherhood protest camp in front of a Cairo mosque,Mursi supporters said they expected the army to provoke violenceto justify its crackdown.
"The army itself will strike. They will use thugs and thepolice," said Sarah Ahmad, a 24-year-old medical student.
Essam El-Erian, another senior Brotherhood politician,accused "the putschists" of trying to recreate a police state."This state will never return, and Egypt will not go backwards,"he said in a televised news conference.
Hesham Kandil, a technocrat who served as Mursi's primeminister, presented an initiative for ending the crisisincluding the release of those jailed since Mursi was detained:the Brotherhood says hundreds of its members have been seized.
He did not say if the Brotherhood endorsed his proposals. (Additional reporting by Asma Alsharif, Yasmine Saleh, NoahBrowning, Tom Finn and Shadia Nasralla; Writing by Tom Perry;Editing by Crispian Balmer and Peter Graff)
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