DHAKA, Bangladesh — The sale of a used car is developing into an unusual criminal case and a potential diplomatic sore point between the United Nations and Bangladesh, whose government has frequently bristled at criticism from the international community.

At the heart of the case is an official named Stefan Priesner, an Austrian who headed the United Nations Development Program in Bangladesh from 2008 to 2012. When he left at the end of his tenure, Mr. Priesner sold his imported sport utility vehicle to a colleague.

But the customs police now say that he evaded $51,732 in taxes owed on the sale. The director general of the customs police, Moinul Khan, said on Thursday that the police were seeking authorization to charge Mr. Priesner with tax evasion and, because he received the proceeds through a foreign bank account, with money laundering.

The government’s real grudge may be not with Mr. Priesner but with the United Nations and other international institutions. The program Mr. Priesner headed worked on electoral reform in Bangladesh, where Prime Minister Sheikh Hasina won the 2014 election essentially by default after major opposition groups boycotted the vote. The next general election is scheduled for next year, and will probably be closely scrutinized.