A report by the UN's Human Rights Office said that the "area clearance operations" launched in the country's Rakhine province in October 2016 "has likely resulted in several hundred deaths", with Rohingya refugees reporting violations amounting to crimes against humanity, AFP reported.
Since that campaign began some four months ago, about 69,000 Rohingya Muslims have fled to neighboring Bangladesh.
"The attacks against the Rohingya population in the area seems to have been widespread as well as systematic, again indicating the possible commission of crimes against humanity", the report noted, adding that forcible displacement as a outcome of violence "has been described in other contexts as ethnic cleansing".
It made the allegations in a damning report compiled after interviews with more than 200 Rohingya refugees who fled from Myanmar to Bangladesh.
During the crackdown in Rakhine, armed members of Burma's security services are said to have rounded up Rohingya men and taken them away in vehicles, before then going from house to house gang-raping or sexually harassing women, and sometimes killing children who cried or tried to protect their mothers.
Myanmar, a mostly Buddhist country where Nobel laureate Aung San Suu Kyi is de facto leader, has denied nearly all allegations of human rights abuses in northern Rakhine and says a lawful counterinsurgency campaign is under way. Among some of the most horrific stories about violence against children, one woman recounted her own raped while her daughter was slaughtered beside her.
Witnesses told the United Nations they had been taunted while they were beaten and mocked over the failure of "Allah" to help.
But the violence follows a long-standing pattern of violations and abuses, systematic discrimination and policies of exclusion and marginalisation against the Rohingya that have been in place for decades in northern Rakhine. "See what we can do?"
The UN's High Commissioner for Human Rights, Zeid Ra'ad al-Hussein, described the "devastating cruelty" against Rohingya children as "unbearable", saying the allegations of babies being stabbed "beg" a reaction from the global community.
The military crackdown in Rakhine, home to more than one million Rohingya, was triggered by October 9 attacks on border guard posts, which Myanmar and the International Crisis Group say were carried out by foreign-backed militants.
The report described "area clearance operations" - gunfire and grenades dropped on villages from helicopters - which are suspected to have killed hundreds.
Aung San Suu Kyi, leader of Myanmar government said, the allegations are invented and has resisted mounting global pressure to protect the minority. "What national security goals could possibly be served by this?"
Zeid urged the government of Buddhist-majority Myanmar - which has generally ignored global appeals to take action - to "immediately halt these grave human rights violations".