Mubarak ruled Egypt with an iron hand and as a staunch ally of the United States, which gives the nation $1.3 billion a year in military aid.
Egyptian reform leader Mohamed ElBaradei -- the former head of U.N. International Atomic Energy Agency and the winner of a Nobel Peace Prize -- said he's been in close contact with the military council and the intelligence services on the one hand and Morsi on the other and has urged them to avoid a showdown.
He said that if Shafik, seen as a candidate of the pro-Mubarak old guard, is declared the winner, "we are in for a lot of instability and violence ... a major uprising." He isn't as worried about a Morsi victory because Shafik supporters are unlikely to take their anger to the streets, he said.
He described the current situation as "a total, complete 100 percent mess."
Muslim Brotherhood lawmakers met with political leaders to discuss plans for a coalition to fight what they believe is a power grab by the military, according to the Facebook page of its Freedom and Justice Party.
"We will NOT accept this coup against democracy," it said, adding that "together, we will march on to complete the revolution."
More than 800 people died and 6,000 were wounded during the uprising that ended Mubarak's 29-year rule in February 2011.
Mubarak and his former interior minister, Habib al-Adly, this month were convicted of ordering security forces to kill anti-government protesters and were given life terms. But other top aides -- as well as Mubarak's two sons, who had been tried on corruption charges -- were acquitted.