UPDATE 1-Egyptians brace for bloodshed as rival protests called
* 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)
CAIRO, July 25 (Reuters) - Supporters of Egypt's deposed president and his opponents predicted blood on the streets ahead of what could be a violent day of mass protests, summoned by the Muslim Brotherhood and the army in a struggle for the country's future.
In a dramatic escalation of rhetoric ahead of a day that both sides view as a potential turning point in Egypt's history, ousted leader Mohammed Mursi's Muslim Brotherhood accused the army of pushing the nation towards civil war and committing a crime worse than destroying Islam's holiest site.
The main anti-Mursi youth protest group replied that its supporters were taking to the streets to "cleanse Egypt".
Army chief General Abdel Fattah al-Sisi, who overthrew the country's first elected leader on July 3, has called on Egyptians to take to the streets on Friday to show their support for action against "violence and terrorism".
Mursi's Brotherhood, organising its own marches on Friday against Sisi, fears the army appeal is a harbinger of a crackdown to wipe out an Islamist movement that has won repeated elections since the fall of autocrat Hosni Mubarak in 2011.
Prime Minister Hazem el-Beblawi, head of the interim cabinet, said there was escalating violence by increasingly well-armed protesters, citing a bomb attack on a police station.
"The presence of weapons, intimidation, fear - this causes concern, especially when there are calls for many to come out tomorrow from different sides," he told a news conference.
After a month in which close to 200 people have died in violence triggered by Mursi's downfall, many fear the protests will lead to more bloodshed.
One security official forecast violence beginning Friday night and stretching into Saturday.
"The history of Egypt will be written on those days," said the official, part of a security establishment that accuses the Islamists of turning to violence.
Reiterating his group's commitment to peaceful protest, senior Brotherhood politician Farid Ismail accused the security services of readying militias to attack Mursi supporters, adding that Sisi aimed to drag Egypt into civil war.
"His definition of terrorism is anyone who disagrees with him," Ismail told Reuters. "We are moving forward in complete peacefulness, going forward to confront this coup."
Muslim Brotherhood leader Mohamed Badie issued a statement accusing Sisi of committing a crime worse than destroying the Kabaa - the site in Mecca to which all Muslims face when they pray - "brick by brick".
But many Egyptians are no less passionately backing the army, determined to see the Brotherhood reined in.
"There are men carrying guns on the street ... We will not let extremists ruin our revolution," said Mohammed Abdul Aziz, a spokesman for Tamarud, an anti-Mursi petition campaign that mobilised protests against his rule.
"Tomorrow we will cleanse Egypt," he told Reuters.
Sisi's speech on Wednesday pointed to the deepening confrontation between the Brotherhood and the military establishment, which has reasserted its role at the heart of government even as it says it aims to steer clear of politics.
Saying it moved against Mursi in response to the biggest popular protests in Egypt's history, the army installed an interim cabinet that plans to hold parliamentary elections in about six months, to be followed by a presidential vote.
The Brotherhood, whose supporters have been camped out in a Cairo suburb for a month, says it wants nothing to do with the transition plan. With Mursi still in military detention at an undisclosed location, there is slim hope for compromise.
The country remains deeply split over what happened on July 3. The Brotherhood accuses the army of ejecting a democratically elected leader in a long-planned coup, while its opponents say the army responded to the will of the people.
Sisi announced the nationwide rallies after a bomb attack on a police station in Mansoura, a city north of Cairo in which a policeman was killed. The government said it was a terrorist attack. The Brotherhood also condemned the bombing, accusing the establishment of seeking to frame it to justify a crackdown.
Since Mursi was deposed, hardline Islamist groups have also escalated a violent campaign against the state in the lawless Sinai Peninsula, with daily attacks on the police and army.
The army says Sisi's speech did not represent a threat to any party, reiterating the military's backing for national reconciliation. The army spokesman said any violence at the forthcoming 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 violence to justify its crackdown.
"The army itself will strike. They will use thugs and the police," 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 prime minister, presented an initiative for ending the crisis including 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, Noah Browning, Tom Finn and Shadia Nasralla; Writing by Tom Perry; Editing by Crispian Balmer and Peter Graff)