A Yemeni army officer was shot dead today by unidentified gunmen in the eastern Yemeni province of Hadramout. An official security source in the province said in a press statement that the gunmen opened machinegun fire at the car in which Colonel Ahmed Al Marfadi, a leader at the 37 Armored Brigade, was traveling in Al Qutn town killing him along with his son and injuring four Yemeni citizens .    The source pointed out that the security agencies started an investigation into the incident in order to disclose the identity of the gunmen, arrest them and bring them to court . The incident comes a week after clashes erupted between Yemeni army forces and gunmen belonging to Al-Qaeda movement in the town of Al Shahr and resulted in the deaths of 13 militants and three soldiers.    Meanwhile, Yemeni authorities today began the implementation of the decision banning movement of motorcycles, which was announced on Friday, after increasing use of motorcycles in recent assassination incidents of security officials and foreigners.