Ho Tan Minh, head of the department office, said he has also instructed the school to take back from students all copies of "On Earth We're Briefly Gorgeous" by Vietnamese-American author Ocean Vuong given to the students.
The school has reportedly taken back 19 copies. The books had been handed out for reference reading to the students before the five-day holiday that began on April 27.
Minh said all schools must be careful when using materials that are not part of the standard curriculum.
The controversy erupted following a post on an online group for parents of the school’s students on Thursday that said a teacher had handed out the novel and the writer were "flabbergasted" to see the contents of the book, and that it had "pornographic content."
ISHCMC said the novel is in a list of reference reading materials in various languages, including Vietnamese, made by the International Baccalaureate program.
"On Earth We’re Briefly Gorgeous" is Ocean Vuong’s debut novel and was nominated for a number of prestigious awards.
Its Vietnamese translation was published in 2021.
The ISHCMC, the first international school in HCMC, was established in 1993.