"As Myanmar is clearly both unwilling and unable to investigate itself, we are now at a stage where the international community must step in to ensure accountability," he added.
Saturday marks one year since Myanmar's security forces cracked down after Rohingya rebels attacked government outposts in Rakhine state, triggering an exodus of at least 700,000 members of the mostly-Muslim community to neighbouring Bangladesh.
The UN and human rights organizations reported numerous times that there was a clear evidence of abuse, with the UN High Commissioner for Human Rights describing it as "ethnic cleansing", bearing all the "hallmarks of genocide".
Santiago said the security forces "killed thousands of Rohingyas, burned their villages to the ground and committed widespread sexual violence".
UN Special Envoy to Myanmar, Christine Schraner Burgener, earlier called for bringing the perpetrators of the crimes against Rohingyas to justice.
Myanmar's State Counsellor and Nobel Peace laureate Aung San Suu Kyi has either played down or denied most of the accusations by international organizations and rights groups.
In November 2017, Myanmar and Bangladesh signed an agreement to repatriate the Rohingya refugees within two years, but the process, which was supposed to have started in January this year, is yet to commence.
Myanmar does not recognize Rohingyas as citizens and considers them Bangladeshi immigrants. The country subjects them to various forms of discrimination, including restrictions on their freedom of movement.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)