President Abed Rabbo Mansour Hadi is facing a new challenge to his authority over the military, with the powerful son of his predecessor disobeying orders and elevating a relative to head a security unit to protect his father. One of Hadi's main goals has been to purge the military of his predecessor Ali Abdullah Saleh's loyalists and family members to enable reforms and restore security to a country that has been in turmoil for more than a year. These steps are seen essential to enable Yemen's armed forces to confront Al-Qaeda-linked militants, who have taken over parts of the south while the country has been distracted by the power struggle in the capital. A senior defense ministry official said Sunday that Saleh continues to meddle in the country's affairs. His son, Ahmed Saleh, commands the powerful Special Forces and Republican Guard, among the country's best trained troops. His appointment of a relative, Tarek Muhammad, to head his father's security unit was direct insubordination to Hadi. Hadi had already demoted Muhammad from head of the Presidential Guards to head a provincial military unit, an order Muhammad and Saleh's son refused to obey. The military official said Hadi has rejected the new appointment. In response, Muhammad refused to hand over his current job during a meeting attended by the UN representative to Yemen. Another relative rejected an order to resign as head of the air force for weeks, finally stepping down last week. That dispute forced a shutdown in Yemen's commercial airport for a day.