Mansour appointed Mohamed ElBaradei, National Salvation Front general coordinator, as vice president, MENA news reported, quoting presidential spokesman Ahmed al-Moslimani.
Beblawi, an economist, served as finance minister in 2011, following the overthrow of former President Hosni Mubarak.
Egypt braced for further violence Tuesday as the Muslim Brotherhood called for an uprising after the killing of 53 backers of deposed President Mohamed Morsi.
The Brotherhood called the killings a massacre, saying soldiers opened fire with live ammunition. The Islamist religious, political and social movement emailed links to YouTube videos it alleged showed civilian victims being carried away from the scene of the mass shooting.
Egypt's official media said 435 people were injured in a clash between the military and supporters of Morsi during dawn prayers in Cairo near where Morsi has been held under house arrest since he was ousted last week.
Egypt's military denied the massacre allegations, saying soldiers defended themselves after they were attacked with guns and Molotov cocktails.
"There are limits for patience," armed forces spokesman Ahmed Ali said. "We hope that our message would reach many of the Egyptian people -- we won't allow any tampering with Egyptian national security."
The military said 42 protesters and a soldier were killed.
Mansour announced a judicial investigation into the killings, but angry crowds massing through the night at a mosque, a focal point for pro-Morsi protests, said the investigation would be meaningless.
He called on Egypt's military to "use maximum restraint responding to protesters, just as we urge all those demonstrating to do so peacefully."
"We also condemn the explicit calls to violence made by the Muslim Brotherhood," Carney said.
Despite Monday's violence, Egypt's military-backed government pressed ahead.
Al-Masry al-Youm reported Tuesday Mansour will not amend the Constitutional Declaration issued Monday, outlining a timeline for Egypt's political transition. The declaration envisions a new Parliament within about six months and a presidential election soon afterward.
The declaration calls for two committees to work out amendments to the Islamist-drafted constitution passed under Morsi, Mansour said late Monday.
A referendum on the new document would be held within four months, he said. Elections for a new Parliament would be held two months after that, in February 2014.
Once the new Parliament convenes, it would set new presidential elections within a week.
The declaration issued Monday also authorizes the president, with consent of the cabinet, to declare a state of emergency for as long as three months. Such a declaration could be renewed by a public referendum.
The spokesman for the ultraconservative Nour Party, which represents Salafi Islamist politicians, said on his Facebook page the party was pulling out of negotiations for a new government to protest the killings.
"We will not be silent on the massacre at the Republican Guard today," Nadar al-Bakkar wrote. "We wanted to stop the bloodshed, but now the blood is being shed in rivers. We withdraw from all talks with the new government."