The Iranian official was questioned by police following complaints from parents but released after invoking diplomatic immunity.
Iran’s embassy denied the allegations, and said they were the result of a “cultural misunderstanding”.
Brazilian Foreign Minister Antonio Patriota called them “very worrying”.
The un-named Iranian diplomat was accused of inappropriately touching girls between 9 and 15 years old at a pool in a private club last weekend, Brazilian media reported.
The father of one of the girls told the G1 website that the diplomat was almost lynched by angry parents before security staff intervened.
“People wanted to kill him,” the unnamed father said.
‘Unacceptable’
The Iranian embassy said the allegations were the result of “a misunderstanding resulting from differences in cultural behaviour”.
It also accused the Brazilian media of deliberately sensationalising the incident.
But Brazilian Foreign Minister Antonio Patriota said he was taking the allegations very seriously and would ask the Iranian embassy for clarification before deciding what action to take.
“Personally I would consider it unacceptable if any Brazilian diplomat conducted himself in this manner in the country in which he was accredited,” Mr Patriota said.
