Egyptian ex-military chief of staff Sami Anan was detained in Cairo on Tuesday, three of his campaign organisers said, after the army summoned him for questioning over his intention to run for president.
The interior ministry could not immediately be reached for comment. The military gave no immediate comment on the alleged detention.
The army had said in an earlier statement, which appeared in text on state TV and was read aloud by a spokesman, that "the armed forces will not overlook the blatant legal violations (Anan) has committed which are a serious breach of the laws of military service."
It said he had announced his candidacy "without getting permission from the armed forces … or taking the steps necessary to terminate his service".
Former army officials must have ended their service and received permission from the military before they can run for political office in Egypt. The statement said Anan had falsified official documents that stated his military service had ended, in order to run.
Anan announced his presidential bid in a video declaration posted on his official Facebook page last week.
He said he was running for president in March's elections to save Egypt from incorrect policies and called on state institutions to maintain neutrality toward all candidates.
Incumbent President Abdel Fattah al-Sisi, himself a former military commander, said last week he would seek a second term.
Anan is not his first potential opponent to find a variety of obstacles being thrown in his path. Other would-be candidates describe concerted efforts – often successful – to kill off their campaigns.