* Fears of violence as rival camps mobilise for rallies
* Interim PM cites fear of casualties
* Brotherhood says aims for biggest protest yet (Adds Qaradawi in paragraphs 10-11)
By Yasmine Saleh and Asma Alsharif
CAIRO, July 25 (Reuters) - Egypt's army threatened onThursday to shoot those who use violence in a stark warningbefore what both sides expect will be a bloody street showdownbetween Islamists and opponents of deposed President MohamedMursi.
An army official said the military had set Mursi's MuslimBrotherhood an ultimatum, giving it until Saturday to sign up toa plan for political reconciliation which it has so far spurned.
The army has summoned Egyptians into the streets on Fridayin an intended turning point in its confrontation with followersof Mursi, the elected leader the generals removed on July 3.
The Muslim Brotherhood, which has maintained a street vigilfor a month with thousands of supporters demanding Mursi'sreinstatement, has called its own crowds out forcounter-demonstrations across Egypt in a "day to remove thecoup".
Both sides have dramatically escalated rhetoric beforeFriday's demonstrations. The Brotherhood accused the army ofpushing the nation towards civil war and committing a crimeworse than destroying Islam's holiest site.
In a Facebook post, the army said it will not "turn its gunsagainst its people, but it will turn them against black violenceand terrorism which has no religion or nation".
A military official said the army had given the Brotherhood48 hours from Thursday afternoon to join the political process.He did not say what would happen if it refuses.
Army chief General Abdel Fattah al-Sisi has called onEgyptians to take to the streets and give him a "mandate" to act against the violence that has convulsed Egypt since heshunted its first freely elected president from power.
The Brotherhood, which has won repeated elections since thefall of President Hosni Mubarak in 2011, accuses the authoritiesof stirring up the violence to justify their crackdown.
Sheikh Youssef al-Qaradawi, an influential Egyptian clericbased in Qatar, issued a religious edict broadcast on Al Jazeeratelevision urging soldiers to disobey orders to kill.
"I call on officers and soldiers in the Egyptian army not tolisten to what al-Sisi says, or anyone else. Do not kill anyone.Do not kill your brothers. It is forbidden," Qaradawi declared.
The main anti-Mursi youth protest group, which has backedthe army, said it would go to the streets to "cleanse Egypt".
The West is increasingly alarmed at the course taken byEgypt, a strategic hinge between the Middle East and NorthAfrica, since protests in 2011 brought down Mubarak and endeddecades of autocratic rule in the most populous Arab state.
Signalling its displeasure, Washington has delayed deliveryof four F-16 fighter jets to Cairo. On Thursday, the White Houseurged the army to exercise "maximum restraint and caution".
The United States has yet to decide whether to call themilitary's takeover a "coup", language that would require it tohalt $1.5 billion it sends in annual aid, mostly for the army.
"CLEANSE EGYPT"
For weeks, the authorities have rounded up some Brotherhoodofficials but tolerated the movement's presence on the streets,with thousands of people attending its pro-Mursi vigil and tensof thousands appearing at its demonstrations.
That patience seems to have run out. Prime Minister Hazemel-Beblawi, head of the interim cabinet installed by the army,said there was growing violence by increasingly well-armedprotesters, 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 nearly 200 people have died in politicalviolence, many fear the protests will lead to more bloodshed.
Past incidents of violence have tended to run through thenight and into the following day. Another security officialforecast clashes beginning Friday night and stretching intoSaturday, the period covered by the army's ultimatum. He alsoindicated that the two-day period was expected to be decisive.
"The history of Egypt will be written on those days," saidthe official, who asked not to be identified.
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."
Brotherhood leader Mohamed Badie accused Sisi of committinga crime worse than destroying the Kaaba - the site in Mecca towhich all Muslims face when they pray - "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 says it wants nothing to do with thetransition plan. With Mursi still in military detention at anundisclosed location, there is slim hope for compromise.
Egypt remains deeply split over what happened on July 3. TheBrotherhood 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 the bombing of apolice station in Mansoura, a city north of Cairo, in which apoliceman was killed. The government called it a terroristattack. The Brotherhood also condemned the bombing, accusing theestablishment of seeking to frame it.
Since Mursi was deposed, hardline Islamist groups have intensified a violent campaign against the state in the lawlessSinai Peninsula, with near-daily attacks on the police and army.
Two more soldiers were killed on Thursday in an attack on acheckpoint, security and medical sources said.
At the Brotherhood protest camp near a Cairo mosque, Mursisupporters said they expected the army to provoke violence tojustify its crackdown. "The army itself will strike. They willuse thugs and the police," said medical student Sarah Ahmad, 24.
Essam wl-Erian, another senior Brotherhood politician,accused "the putschists" of trying to recreate a police state,telling a televised news conference: "This state will neverreturn, and Egypt will not go backwards." (Additional reporting by Tom Perry and Maggie Fick, NoahBrowning, Tom Finn, Shadia Nasralla, Asma Alsharif and OmarFahmy; Writing by Tom Perry and Matt Robinson; Editing by PeterGraff and Alistair Lyon)
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