The mainly Muslim African state of The Gambia had asked the court to impose the emergency measures - pending a full case that could take years - following a bloody military crackdown by Myanmar in 2017 that sent around 740,000 Rohingya fleeing into neighbouring Bangladesh.
The ICJ's presiding judge, Abdulqawi Ahmed Yusuf, said that "the court was of the opinion that the Rohingya in Myanmar remain extremely vulnerable". Thousands are suspected to have been killed in the crackdown and refugees brought widespread reports of rape and arson in Rakhine state by Myanmar's military and local Buddhist militias.
The court ordered Myanmar to "take all measures within its power to prevent the commission of all acts" described by the 1948 UN Genocide Convention, under which Gambia brought the case. These acts included "killing members of the group" and "deliberately inflicting on the group conditions of life calculated to bring about its physical destruction in whole or in part."
The court ordered Myanmar to report back within four months, and then every six months after that. It also told Myanmar to prevent the destruction of any evidence of crimes against the Rohingya. Myanmar however remained defiant, with its foreign ministry insisting after the ruling that "there was no genocide in Rakhine".
"The unsubstantiated condemnation of Myanmar by some human rights actors has presented a distorted picture of the situation," it said in a statement, adding that Thursday's decision "in no way prejudges" the longer-term legal case.
Nobel peace laureate Suu Kyi - who was widely criticised for her defence of the same military that once locked her up for years - said earlier Thursday that some Rohingya refugees may have "exaggerated" abuses. "The international justice system may not yet be equipped to filter out misleading information before shadows of incrimination are cast over entire nations and governments," she wrote in an opinion piece in the Financial Times.