Please be advised that the U.S. Embassy, Dhaka, is not allowed to issue a drivers license to U.S. citizens. However, if any U.S. citizen wants to get a driver license in Bangladesh, s/he first needs to get a Bangladeshi issued regular driver license from Bangladesh Roads Transport Authority (BRTA). To know more about the process of obtaining a driver license and contacting their office, please visit http://www.bangladesh.gov.bd/index.php?option=com_content&task=category&id=146&Itemid=27.
After receiving that license they can contact the Automobile Association of Bangladesh to convert it to an International Driving Permit. Altogether, the process might take about four months. To know more about the process of obtaining an International Driver License and contacting their office, please visit http://www.brta.gov.bd/index.php/international-driving-permit.