Supporters of General Sami Anan said he was held today after being summoned to Cairo for questioning over his political ambitions. On 23 January, the Armed Forces announced through a statement published on its official Facebook page that Sami Anan must be interrogated and face legal action for announcing his nomination in the presidential elections "without obtaining the permission of the Armed Forces".
That paves the way for President Abdel-fattah al-Sisi to run for a second term in March without any major challengers.
He had yet to present his papers to the election committee. He said poor Egyptians had been bribed to sign documents supporting el-Sissi's candidacy and that the election commission had ignored some of his campaign's requests, including one for the removal of billboards declaring support for el-Sissi that have sprang up before the official start of campaigning.
Sisi has been in power since 2013, after leading a military coup that ousted former leader Mohammed Morsi from power, before winning by a landslide in the 2014 presidential election.More news: Milwaukee Bucks: 5 reasons Jason Kidd was sacked
Mr Anan, who served as the army's chief of staff from 2005-2012, announced his intention to stand against President Sisi on social media earlier this month.
It also said Anan's announcement on Saturday "constitutes direct incitement against the armed forces with the intent of causing a rift between it and the great Egyptian people".
Ali was the only serious would-be candidate to challenge President Abdel-Fattah el-Sissi.
The arrest all but ended the presidential ambitions of the ex-general, who became the latest in a series of potential contenders who have dropped out or been driven from the presidential campaign.More news: CDC spokesperson calls flu season 'unprecedented'
Egypt's military announced earlier Tuesday it will investigate Annan for allegedly forging documents and breaching army regulations.
When he announced last week he meant to run, he listed Egypt's achievements in his first term and said: "Building the state takes 16 to 20 years, I am trying to finish it in eight years, God willing". After announcing his candidacy from self-imposed exile in the United Arab Emirate, the former Egyptian Prime Minister Ahmed Shafik was returned to Cairo by Emirati authorities.
The case was pursued "for nothing except to provide a legal excuse that would prevent us from running", he said.
Ali meanwhile has appealed a three-month sentence in September on charges of offending public decency, in relation to a photograph that Ali says was fabricated and that appeared to show him making an obscene gesture outside a court house. His candidacy also could have drawn a sizable protest vote from Egyptians struggling under high prices resulting from el-Sissi's ambitious reform program to overhaul the battered economy.More news: Australia to launch full-scale review into recent ODI failures
His arrest now leaves only one other candidate, Khaled Aly, in the race against President Sisi.