Top officials and relatives of Lt. Gen. Sami Anan said he was taken from his car Tuesday and detained by authorities. His arrest came soon after Egypt's military released a statement that was read on state television accusing him of seeking presidential office "without getting prior approval from the armed forces."
Anan was also accused of "forging documents" that claimed he had terminated his military service and of "incitement against the army" by announcing he would challenge Sissi, the country's former military chief, in the election. The statement added that Anan committed "violations that require investigation."
"This goes far beyond these charges," said Mostafa Elshall, the director of Anan's office and a close friend, suggesting the measures were intended to deter Anan's presidential bid.
Shortly after Anan's arrest, his campaign team announced that it had stopped his presidential campaign until further notice, "for the safety of all citizens dreaming of change."
Anan is the latest candidate to exit the presidential race amid claims of intimidation by authorities. Other candidates have complained of pro-government media attacks, harassment of supporters and a nomination process tilted toward Sissi.
Last week, Mohamed Anwar al-Sadat, the nephew of assassinated president Anwar Sadat, abruptly pulled out of the contest, citing concerns about his safety and about the prospects for fair and transparent elections. Another candidate, Col. Ahmed Konswa, announced his intention to run but was then sentenced to six years in prison. He was also charged with violating military rules.
Ahmed Shafik, a former prime minister and air force chief, was Sissi's most prominent opponent. But he also withdrew, saying he had spent too much time outside the country.
With Anan's exit, the only viable candidate appears to be human rights lawyer Khaled Ali. But he is embroiled in a legal case that could disqualify him.
Egypt's electoral commission has publicly promised to run the election in an independent and transparent manner. But many Egyptians expect that Sissi, who announced his decision to run for a second term last week, will be reelected and tighten his grip on power.
The March vote marks the third presidential election since the 2011 Arab Spring revolt, which toppled President Hosni Mubarak. In 2013, Sissi helped orchestrate the overthrow of the country's elected Islamist president, Mohamed Morsi, and was elected president the following year.
Sissi's popularity has been sinking as the result of an anemic economy that has led to austerity measures, rising prices and lowered subsidies. His government has been cracking down on opponents and activists, jailing thousands while shutting down hundreds of websites deemed critical of the government.
The security forces, meanwhile, are confronting an Islamic State affiliate, based in North Sinai province, that has steadily killed police and soldiers and staged numerous attacks on civilians throughout the country.
Anan's arrest came a week after he announced his presidential aspirations on his official Facebook page, promising reform. Now, his campaign workers do not know when they will see him again.
"I think it is very unlikely he would be released on bail pending investigations," Elshall said while at the office of the military prosecutor. "We're waiting to see what will happen with Anan."