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Egypt announced Tuesday that former Finance Minister Hazem el-Beblawi is the country's new interim prime minister and opposition leader Mohamed ElBaradei is now vice president, despite the Muslim Brotherhood's rejection of a timetable for a political transition.

Ahmed el-Musalamani, the spokesman of interim Egyptian President Adly Mansour, made the announcements Tuesday after days of political stalemate over the prime minister post. Last week, ElBaradei was on the verge of being named prime minister, but at the last minute the hard-line Islamist party Al-Nour, who was involved in the discussions, blocked ElBaradei's appointment.

Al-Nour officials said Tuesday that they approved Beblawi's appointment, but said they were still reviewing ElBaradei, Reuters reported.

Egypt's army chief Abdel-Fattah el-Sissi said in thinly veiled warning to the Al-Nour party that the military will not accept political "maneuvering."

"The future of the nation is too important and sacred for maneuvers or hindrance, whatever the justifications," el-Sissi said on state TV.

El-Beblawi, who is in his 70s, served as finance minister in one of the first cabinets formed after the 2011 uprising forced Hosni Mubarak from power and the military stepped in to rule.

He resigned in protest in October 2011 after 26 protesters, mostly Christians, were killed by troops and security forces in a crackdown on their march.

The announcements came after the Muslim Brotherhood rejected a plan announced by Mansour for amending the country's constitution and setting new presidential elections. The group also called for more protests after a day of shootings that left at least 51 dead.

Under the plan put forward by Mansour late Monday, two panels would be appointed to make amendments to the Islamist-backed constitution passed under former President Mohammed Morsi's government. Those changes would be put to a referendum within about 4½ months. Parliamentary elections would be held within two months after that, and once the new parliament convenes it would have a week to set a date for a presidential election.

The swift issuing of the plan reflected a drive on the part of Egypt's military-backed interim leadership to push ahead with a post-Morsi political plan despite Islamist opposition.

President Barack Obama's spokesman, Jay Carney, said Tuesday that the White House was "cautiously encouraged" by the announcement of the plan and called for all parties to be included in the electoral process.

But Essam el-Erian, a senior Muslim Brotherhood member, said Tuesday on his official Facebook page that the transition plan will take the country back to "square one" and vows that the Brotherhood will not drop its push to reinstate deposed Morsi, who was a longtime member of the group. The Muslim Brotherhood contends that Morsi was removed by a coup and that everything that follows is illegal.

The streets of Cairo were quiet on Tuesday, Reuters reported, but the group has called for additional protests later in the day, renewing fears of more violence.

Meanwhile, the United Arab Emirates has offered a $1 billion grant and a $2 billion no-interest loan to Egypt's new government, according to the WAM news agency. Saudi Arabia's finance minister also said the kingdom has pledged $5 billion in grants and loans.

The "constitutional declaration" announced by  Mansour late on Monday coincided with the nation's deadliest day since Morsi's July 3 ouster, with more than 50 of his supporters killed by security forces as the country's top Muslim cleric raised the specter of civil war.

The killings further entrenched the battle lines between supporters and opponents of Morsi, and the ousted leader's Brotherhood backers called for an uprising, accusing troops of gunning down protesters. The military blamed armed Islamists for provoking its forces.

The shootings began during a protest by about 1,000 Islamists outside the Republican Guard headquarters where Morsi, Egypt's first freely elected leader, was detained last week. Demonstrators and members of the Brotherhood said troops descended on them and opened fire unprovoked as they finished dawn prayers.

"I was in the last row praying. They were firing from the left and right," said Nashat Mohammed, who had come from southern Egypt to join the sit-in and was wounded in the knee. "We said, 'Stop, we're your brothers.' They shot at us from every direction."

After a battle lasting about three hours, at least 51 protesters were killed and 435 wounded, most from live ammunition and birdshot, emergency services chief Mohammed Sultan told to the state news agency.

At a nationally televised news conference, Army Col. Ahmed Mohammed Ali said police and troops came under "heavy gunfire" at around 4 a.m. and attackers on rooftops opened fire with guns and Molotov cocktails. A soldier and two policemen were killed, and 42 in the security forces were wounded, eight critically, he said.

While he said troops had a right to defend the facility, Ali did not directly explain how the protester deaths occurred. He expressed condolences but offered no apologies for the deaths.

A collection of videos of the clashes provided by the military to Egyptian TV showed protesters on rooftops lobbing projectiles at troops below, including firebombs and toilet seats. It also showed some armed protesters firing at close range at the troops, but it did not show what the military did. It was also not clear at what time in the fighting the videos were shot. It included aerial views of the clashes.

Several witnesses from outside the protest said the gunfire started when troops appeared to move on the camp.

University student Mirna el-Helbawi told The Associated Press that she watched from her 14th floor apartment overlooking the scene, after she heard protesters banging on metal barricades, a common battle cry. El-Helbawi, 21, said she saw troops and police approaching the protesters, who were lined up on the street behind a make-shift wall. The troops fired tear gas, the protesters responded with rocks, she said.

Soon after, she heard the first gunshots and saw the troops initially retreat backward — which she said led her to believe the shots came from the protester side. She saw Morsi supporters firing from rooftops, while the troops were also shooting.

The Freedom and Justice party, the Muslim Brotherhood's political arm, called on Egyptians to rise up against the army, which it accused of turning Egypt into "a new Syria."

The sole Islamist faction that backed Morsi's removal, the ultraconservative Al-Nour Party, suspended its participation in talks on forming a new leadership for the country. The group is now torn by pressure from many in its base, furious over what they saw as a "massacre" against Islamists.

Reeling from scenes of bloodied protesters in hospitals and clinics, many with gaping wounds, some of Egypt's politicians tried to push new plans for some sort of reconciliation in the deeply polarized nation.

Sheik Ahmed el-Tayeb, the grand imam of Al-Azhar, the most prominent Sunni Muslim institution, demanded that a reconciliation panel with full powers immediately start work and that those detained in recent days be released. Five prominent Brotherhood figures have been jailed since Morsi's fall, and Morsi himself is held in detention in an unknown location.

Struggling whether to fully bolt from the new leadership, the ultraconservative Al-Nour Party denounced what it called incitement against fellow Islamists. Speaking to Al-Jazeera TV, the party's chief Younes Makhyoun raised the possibility of calling a referendum on Morsi as a compromise measure.

There were multiple calls for an independent investigation into the bloodshed as a way to establish the truth and move forward.

Egypt's escalating crisis could further complicate its relations with Washington and other Western allies, which had supported Morsi as the country's first freely elected leader and now are reassessing policies toward the military-backed group that forced him out.

Still, the White House said Monday that cutting off the more than $1 billion in annual aid to Egypt was not in the U.S.' best interests, though it was reviewing whether the military's moves constitute a coup — which would force such a measure under U.S. law.

The Associated Press contributed to this report.