Egypt's leftist leader, the ex-army chief's main rival in next month's presidential election, Wednesday urged all revolutionary groups to unite, as a liberal party threw its weight behind him.
Hamdeen Sabbahi, who has emerged as the main challenger to former field marshal Abdel Fattah al-Sisi in the May 26-27 vote, also reiterated that the military should stay out of politics.
Sabbahi came third in the 2012 presidential election won by Islamist Mohamed Morsi, whom Sisi ousted last July.
On Wednesday, Sabbahi urged all groups that joined the 2011 uprising against Hosni Mubarak to unite.
"I tell them, now is the time to unify our efforts and define our objectives and prove our ability to win," the prominent opposition leader said at a news conference.
His plea for unity came as the liberal Al-Dostour party, founded in 2012 by former vice-president and opposition leader Mohamed ElBaradei, threw its weight behind him.
Party chief Hala Shukrallah, speaking at the news conference with Sabbahi, said Al-Dostour conducted an internal poll before deciding to back him.
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Sabbahi, who was jailed several times under Mubarak and his predecessor Anwar Sadat, said his group will taste "one of two victories".
He saw these as either "rule that instals a successful state which expresses the goals of the revolution, or a strong opposition that fights for the same goals".
Sabbahi also reiterated that Egypt's military must remain aloof of politics.
The army's role is to "protect the nation... and confront external and internal risks without interfering in politics", he said.
His spokesman Maasoum Marzouk admitted, however, that Sabbahi still needed several hundred signatures to register his candidacy officially as required by the electoral law.
The law stipulates that in order to be officially registered a candidate needs at least 25,000 signatures from citizen supporters.
Critics of Sisi, who is widely expected to win the election, say that under him Egypt would return to the autocratic rule of the Mubarak era.
Sisi has dismissed such fears, triggered after the military-installed authorities jailed several prominent protesters who led the anti-Mubarak uprising.
Sabbahi has also said that Egypt would never return to "Mubarak's corruption or Morsi's authoritarianism".