CAIRO - Former Egyptian military chief of staff General Sami Anan, who was detained in January after announcing plans to compete in a presidential election, is in critical condition in hospital, two sources close to his family said on Monday.Anan, 70, was admitted to the intensive care unit at a military hospital in Cairo's Maadi suburb on Saturday and is on life support after suffering a chest infection and back problems that have impaired his ability to move, the sources said."He is in a very critical situation in the intensive care unit," one of the sources told Reuters.Military spokesman Colonel Tamer al-Rifai was not immediately available for comment.The sources said Anan, who was detained in January, was held in a military prison until he suffered a stroke more than two months ago and was moved to the military hospital. They said his health had been improving and that the setback was a surprise.Anan's family last visited him about a week ago and said he was in good health, the sources said.Egyptian President Abdel Fattah al-Sisi was re-elected for a second term in March, winning 97 percent of the vote with turnout of 41 percent. The election featured only one other candidate, an ardent Sisi supporter, after opposition contenders halted their campaigns in January.Anan, seen as Sisi's main challenger, was arrested and halted his presidential bid after the army accused him of running for office without permission, which it said was a breach of military law. Anan's spokesman denied that he had broken any laws.