Former Egyptian intelligence chief Omar Suleiman said on Friday he would run for president if supporters complete his paperwork within a day, putting one of ousted leader Hosni Mubarak's closest allies back in the race days after he ruled himself out.

Nominations close on Sunday for Egypt's first free presidential race, which is set to pit Islamists against those who served under the ousted president.

Suleiman, 74, served for years as Mubarak's head of military intelligence and General Intelligence Service.

Mubarak named him vice-president in January last year during a popular uprising, and attempted to transfer powers to him before quitting in disgrace.

In a statement circulated by campaign aides, Suleiman said public demand had convinced him to run if he could obtain the necessary registration of 30,000 supporters by Saturday.

"I have been shaken by your strong position," said the statement, addressed to 'citizens of Egypt'. "The call you have directed is an order and I am a soldier who has never disobeyed an order."

"Your call and your faith in my ability is an honor," it added. Suleiman had said on Wednesday he would not run.

Hundreds of Suleiman supporters staged a rally in Cairo on Friday carrying banners reading 'Suleiman, save Egypt' and 'We don't want the Islamists'.

As a candidate, he could appeal to the army and voters worried about the prospect of a rise to power by Islamists that were repressed by Mubarak.

Earlier on Friday, thousands of supporters of Salafi Islamist Hazem Salah Abu Ismail demonstrated against what they called an official plot to stop the ultraconservative sheikh from contesting the presidential election.

Abu Ismail had emerged as one of the frontrunners for the race but the electoral commission said on Thursday it was checking information his mother had a U.S. passport - potentially disqualifying him.

His climbing popularity has alarmed secular Egyptians afraid of an ultra-conservative ruler at the helm and compounded worries that Islamists were dominating Egypt's institutions after they won a majority of seats in parliament. Islamists now control an assembly writing the new constitution.

'CONVINCE HIM TO RUN'
Suleiman and his aides have been giving mixed signals for weeks about whether he would actually stand. His aides seem to want to create the impression that he is a reluctant figure responding to a groundswell of public support.

"Suleiman decided to run because anyone who loves this country has been begging him to do so. He has even had to switch off his phone because of the number of calls he was receiving to convince him to run," campaign aide Saad Abbasy told Reuters.

Egyptian activists have been speculating that Suleiman would emerge as a candidate backed by the ruling military council that Mubarak handed power to. They believe Suleiman would guard the army's economic interests and budget from civilian oversight.

He would not be the only military figure and former Mubarak associate on the ballot. Ahmed Shafiq, 70, a former air force commander and civil aviation minister who was appointed as Mubarak's last prime minister in the final days of the uprising, has also announced his candidacy.

About a dozen other candidates are also standing, including former Arab League chief Amr Moussa and several Islamists.

Abu Ismail's followers accuse Western countries and Egypt's ruling generals of trying to force the ultra-conservative off the ballot after an opinion poll tipped him for second place.

Perhaps encouraged by Abu Ismail's popularity, the more pragmatic Muslim Brotherhood also announced it would field a candidate after earlier saying it would not.

"Abu Ismail is the man most fit for the job," said Salah el-Saed, a 21-year old university student, as he held up a banner showing the smiling candidate in Cairo's Tahrir Square.

"My faith in him has not and will not be shaken by these false lies. This is a conspiracy. They want someone like Suleiman to win," he added.

Some banners at the Islamist protest called for the hanging of Field Marshal Mohamed Hussein Tantawi, head of the ruling council, if the council attempted to falsify the election.

Under Egypt's election rules, both of a candidate's parents must be Egyptian and with no dual citizenship. The electoral commission said it was waiting for information from the foreign ministry before Abu Ismail's registration could be confirmed.

Abu Ismail's campaign has said it will file a suit against the Interior Ministry because it refused to provide any documents on his mother's citizenship.

The protesters, some wearing face masks with Abu Ismail's picture, chanted 'She is Egyptian, she is Egyptian' and 'Hazem! Hazem! We want Hazem!'