RIO DE JANEIRO — The head of Brazil’s Olympic Committee was detained on Thursday as part of an investigation into allegations that bribes helped secure the selection of Rio de Janeiro as the host of the 2016 Summer Games.

Carlos Arthur Nuzman, the head of the committee, was accused of failing to declare assets held abroad, including 16 bars of gold stashed in Switzerland.

In a statement, prosecutors said that Mr. Nuzman had disclosed those holdings only in amended tax filings submitted after investigators raided his home early last month as part of an international investigation code-named Operation Unfair Play.

Prosecutors say Mr. Nuzman’s wealth grew exponentially over the past 10 years. He has led Brazil’s Olympic Committee for more than two decades.