The White House on Monday said an investigation into the recent poisoning of schoolgirls in protest-hit Iran could fall under the mandate of the UN.
Several hundred cases of gas poisoning have been reported in more than 52 schools across Iran since the end of November, according to an official count.
They come more than five months after the start of protests, called riots by Tehran, that were sparked by the death of Iranian Kurd Mahsa Amini, 22, after her arrest for wearing her hijab "improperly".
"If these poisonings are related to participation in protest then it is well within the mandate of the UN independent international fact-finding mission on Iran to investigate," White House spokeswoman Karine Jean-Pierre said.
Ms Jean-Pierre was referring to the body established in November to investigate human rights abuses in Iran.
"There must be a credible independent investigation, accountability for those responsible," she said, calling the poisonings "unconscionable".
For more than three months, hundreds of female pupils have reported symptoms such as shortness of breath, nausea and vertigo after detecting "unpleasant" or "unknown" odours, with some girls being admitted to hospital.
The incidents have sparked fear among parents and calls for authorities to act, with deputy health minister Younes Panahi saying recently the suspected attacks were aimed at shutting down education for girls.
Iran's supreme leader Ayatollah Ali Khamenei on Monday said perpetrators should face "severe punishment", according to his website.
Iranian officials have not announced any arrests so far.