Three candidates knocked out of Egypt's presidential election in the first round said on Monday that violations had rendered the result invalid, further challenging the legitimacy of the vote less than two weeks before the run-off. 

In a joint statement, the campaigns of third-placed Hamdeen Sabahy, fourth-placed Abdel Moneim Abol Fotouh and seventh-placed Khaled Ali listed irregularities which included an allegation that the ballots of 1.5 million voters systematically had been rendered void. 

The criticism casts another shadow over the last stage of Egypt's transition to civilian rule due to culminate with the army handing power to the new president on July 1. 

The June 16-17 run-off between Ahmed Shafiq, Hosni Mubarak's last prime minister, and Mohamed Mursi, the Muslim Brotherhood's candidate, is expected to go ahead regardless: the body overseeing the election has thrown out complaints. 

However, with demonstrators staging a third day of protests over the controversial outcome of the trial of Mubarak and his top aides, the fresh accusations of electoral fraud added to the doubts surrounding the already messy transition. 

The complaints were based on the official logs of the vote count which by law are distributed to the candidates, the statement said. It added that Shafiq's voters had included hundreds of members of the security forces, who are not entitled to vote, and people listed as dead. 

Ballots cast in favour of Sabahy had been found loose outside polling stations in five provinces, it added.  

"After coordination, the campaigns of the three candidates declare the invalidity of the result of the first round of the presidential election," the joint statement declared. 

Sabahy formally asked a Cairo court to suspend the whole election and order a re-run, a judicial source said, but the legal challenge was unlikely to disrupt the election timetable. 

International monitors received their accreditation too late to monitor most of the election campaign but gave guarded approval of the voting process despite several irregularities.  

But deeply disappointing to the revolutionary youth who took to the streets last year to end Mubarak's three-decade rule, the election result triggered new protests fueled by concern that one of the deposed leader's aides might replace him.  
  
MASS PROTEST CALLED FOR TUESDAY 

The Muslim Brotherhood has been reaching out to other reform-minded politicians in an effort to build broad support for Mursi's presidential bid, presenting him as a bulwark against any revival by Mubarak's old guard. 

The Brotherhood has long been part of the movement for democratic change in Egypt but is now itself the focus of suspicion on the part of many Egyptians who believe it to be power hungry. The group's critics have urged it to make clear, written power-sharing guarantees to secure broader support. 

Mursi met Sabahy and Abol Fotouh on Monday in a meeting that produced a joint call for participation in a mass protest on Tuesday but no sign of the kind of agreement that might help rally broad support to the Brotherhood's side in the run-off.  

The participants agreed to keep up pressure for the implementation of a law passed by parliament in April and that would have stopped Shafiq from running for the presidency in the first place on the grounds he had served as Mubarak's premier. 

They also called for a just and urgent trial for Mubarak and "the symbols of his regime", according to a joint statement. 

The outcome of the Mubarak trial has added to the turbulence facing Egypt. The former president was sentenced to life in prison, along with his former interior minister, over the deaths of protesters killed in the uprising that swept him from power. 

But top aides were acquitted because of a lack of evidence, raising concern that Mubarak himself could get off at appeal.  

Several hundred protesters blocked traffic in Tahrir Square - the cradle of the anti-Mubarak uprising - for a third day on Monday in a demonstration that has fused anger at the outcome of the trial with protests at the result of the presidential vote. 

"The martyrs didn't get their rights and their mothers are weeping," said Fawzi Fawzi, a 33-year-old teacher who was in the square on Monday morning.