The UN’s highest court ordered Myanmar on Thursday to do everything in its power to prevent the genocide of Rohingya Muslims, as international justice stepped into the crisis for the first time.

In a unanimous ruling, the International Court of Justice rejected arguments made by Myanmar’s civilian leader Aung San Suu Kyi in The Hague last month and set out urgent steps for the predominantly Buddhist nation to end the violence.

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: “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 The 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.

However, Myanmar 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 on 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.

But The Gambia hailed the decision as a major step forward by the court, which was set up after World War II to rule in disputes between UN member states.

“This is a historic day today, not just for international law, for the international community, but especially for the Rohingya,” Gambian justice minister Abubacarr Tambadou told reporters outside the court.

The African state’s case was supported by the 57-nation Organisation for Islamic Cooperation, Canada and the Netherlands.