Egypt's ruling Freedom and Justice Party has said that "a full military coup" was under way to remove President Mohamed Morsi from power, after an army deadline urging him to meet the protesters' demands expired.
Gehad El-Haddad, a spokesperson for the Muslim Brotherhood and senior adviser to the Freedom and Justice Party, said on Wednesday that armoured personnel carriers were on the move around the outskirts of Cairo and that "some high ranking members of the Brotherhood have been arrested".
Haddad also told Al Jazeera that communication with Morsi was cut off, saying that he could not confirm nor deny whether the president was moved from the Republican Guard Headquarters in the capital.
The statement came as hundreds of thousands of anti-government portesters rallied across the city, flooding Tahrir Square in the centre, the main hub of the opposition coalition movement.
The army said a roadmap for Egypt's political future will be unveiled at around 19:30 GMT, with state media reporting that the plan sets a tight schedule for new elections.
State television said opposition leader Mohamed ElBaradei and the heads of the Coptic Church and Al-Azhar - Sunni Islam's highest seat of learning - would present the roadmap for the country's future.
ElBaradei, Pope Tawadros II and Al-Azhar Grand Imam Ahmed al-Tayyeb had been in talks with the military over the transition from the rule of the Islamist president, military sources said earlier.
According to the official MENA news agency, the roadmap is to consist of a "short" transition period followed by both presidential and parliamentary.
The army reportedly also slapped a travel ban on the president and his Islamist allies by sending a list of names to airport security, security sources told Reuters news agency.
The list included Muslim Brotherhood leaders Khairat el-Shater, Essam el-Erian and at least 40 other Islamist leaders, the sources tsaid.
Egyptian paratroopers began fanning out near an army barracks where the embattled president was reportedly working, as the country waited eagerly for an expected announcement by the armed forces that may unseat Egypt's first democratically elected president.
The army also erected barbed wires and barriers around the barracks and deployed armoured vehicles and troops to prevent his supporters marching from a nearby rally to his palace.
Troops also moved into the area near the Rabaa Adaweya mosque, where tens of thousands of supporters of Morsi's Muslim Brotherhood were rallied to support the president and what they call constitutional legitimacy.
The army said in an official statement that it was securing the area and denied what it said were reports that it was attacking Morsi's supporters, saying: "The Egyptian army belongs to all Egyptians".
Earlier on Wednesday, Morsi proposed a consensus government as a way out of the country's crisis.
"The presidency envisions the formation of a consensus coalition government to oversee the next parliamentary election," his office said on Wednesday in a statement on Facebook.
The statement reiterated that Morsi held opposition parties responsible for obstructing a political initiative that would also set up a panel to prepare amendments to the constitution passed into law last December.
Earlier, the army leaked details of the roadmap that included overthrowing Morsi, scrapping a draft constitution and forming a government of independents headed by an army general.
The arm said it had to intervene after unprecedented rallies by million of Egyptians at the weekend to demand Morsi step down.
The United States, on Wednesday said it was "very concerned" about the situation in Egypt.
The situation remained fluid and the United States could not confirm whether a coup by Egypt's military was under way, State Department spokesperson Jen Psaki told reporters.
"We do ... remain very concerned about what we're seeing on the ground," Psaki told reporters, adding that a peaceful political resolution would be the best option.