A Palestinian teenager admitted to Harvard says he has been denied entry to the US after officials objected to his friends' social media posts.
Ismail Ajjawi, who lives in Lebanon, says he was questioned for hours after arriving at Boston's airport on Friday.
Mr Ajjawi, 17, says his visa was cancelled after immigration officials searched his phone and laptop.
Despite his protests that he had nothing to do with the posts, he was found "inadmissible" to the US.
Customs and Border Protection (CBP) spokesperson Michael McCarthy says the decision was made "based on information discovered during the CBP inspection".
Mr McCarthy declined to comment on the specifics of the case, citing confidentiality clauses.
Mr Ajjawi, who was awarded a scholarship to study in the US, has since returned to Lebanon.
Harvard says "the university is working closely with the student's family and appropriate authorities to resolve this matter" before classes being on 3 September.
Mr Ajjawi is also being provided with legal assistance by a US non-profit organisation.
In June, the US Department of State said nearly all applicants for US visas would have to submit their social media details under newly adopted rules.
It said travellers would have to submit social media names and five years' worth of email addresses and phone numbers.
The administration of President Donald Trump first proposed the rules in March 2018. Officials at the time estimated that the new regulations would affect 14.7 million people annually.
Certain diplomatic and official visa applicants are exempt from the stringent new measures.