Egyptian politicians, including three of the losing candidates in the first round of the presidential election, joined forces on Monday with youth groups demanding the suspension of a second-round runoff.
The joint call is aimed at putting pressure on election frontrunner Ahmed Shafiq, a former Hosni Mubarak premier, who is due to square off against Muslim Brotherhood candidate Mohammed Morsi on June 16-17.
Leftist Hamdeen Sabbahi and moderate Islamist Abdel Moneim Abul Fotouh, who came third and fourth respectively in last month's polls, inked the statement along with fellow candidate Khaled Ali.
They are demanding that the runoff be suspended until the implementation of the so-called political isolation law which bans Mubarak-era officials from standing for office.
Shafiq was initially barred from standing in the presidential race but in late April the electoral commission accepted an appeal from Mubarak's last premier against his disqualification.
The political isolation law was adopted by the Islamist-dominated parliament in April.
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Last week, Al-Akhbar newspaper said that Egypt's top court was expected to rule on the constitutionality of the law on June 11 -- five days before the runoff is due to be held.
Citing judicial sources it did not identify, the newspaper said "the Supreme Constitutional Court will rule on the constitutional challenge to the political isolation law on June 11."
The case could have serious implications for Shafiq, who served briefly as Mubarak's last prime minister before the veteran leader was ousted early last year in a popular uprising.
In the first round of the election, Islamist presidential hopeful Mursi won 24.77 percent of the votes, slightly ahead of Shafiq's 23.66 percent.
Sabbahi came third with 20.71 percent, ahead of Abul Fotouh with 17.47 percent, while former foreign minister Amr Mussa was fifth with 11.12 percent. Khalil trailed behind.
Shafiq is reviled by the youth activists who spurred the revolution and last week unknown attackers set fire to his Cairo campaign headquarters.
Leftists, liberals and Islamist politicians as well as youth groups signed Monday's statement.