Petraeus sex scandal threatens to engulf Gen Allen
General Allen was put under investigations after FBI agents probing email threats sent by Petraeus's mistress stumbled upon messages the US commander sent to another married woman at the centre of controversy.
US President Barack Obama has put on hold the nomination of Allen as the next commander of the US European Command as the US Defence Secretary Leon Panetta in a statement said that FBI has referred to him the matter involving General John Allen.
The ripples in the US military came as Panetta demoted a former head of the Africa command on charges of lavish travel and spending.
General William Ward, former Commander of US Africa Command, would now be retired at the grade of Lieutenant General, the Pentagon Press Secretary George Little said.