(reuters) -- The allegation in a report by the New York-based rights group echoes an accusation by Pramila Patten, the U.N. special envoy on sexual violence in conflict, earlier this week. Patten said sexual violence was "being commanded, orchestrated and perpetrated by the Armed Forces of Myanmar."

Myanmar's army released a report on Monday denying all allegations of rape and killings by security forces, days after replacing the general in charge of the operation that drove more than 600,000 Rohingya Muslims to flee to Bangladesh.

The United Nations has denounced the violence as a classic example of ethnic cleansing. The Myanmar government has denied allegations of ethnic cleansing.

Human Rights Watch spoke to 52 Rohingya women and girls who fled to Bangladesh, 29 of whom said they had been raped. All but one of the rapes were gang rapes, Human Rights Watch said.

"Rape has been a prominent and devastating feature of the Burmese military's campaign of ethnic cleansing against the Rohingya," said Skye Wheeler, women's rights emergencies researcher at Human Rights Watch and author of the report.

"The Burmese military's barbaric acts of violence have left countless women and girls brutally harmed and traumatized," she said in a statement.

Human Rights Watch called on the U.N. Security Council to impose an arms embargo on Myanmar and targeted sanctions against military leaders responsible for human rights violations, including sexual violence.

The 15-member council last week urged the Myanmar government to "ensure no further excessive use of military force in Rakhine state." It asked U.N. Secretary-General Antonio Guterres to report back in 30 days on the situation.

Myanmar has said the military clearance operation was necessary for national security after Rohingya militants attacked 30 security posts and an army base in Rakhine state on Aug. 25.

Myanmar is refusing entry to a U.N. panel that was tasked with investigating allegations of abuses after a smaller military counteroffensive launched in October 2016.

Hala Sadak, a 15-year-old from Hathi Para village in Maungdaw Township, told Human Rights Watch that soldiers had stripped her naked and then about 10 men raped her.

She told Human Rights Watch: "When my brother and sister came to get me, I was lying there on the ground, they thought I was dead."

(Photo:  Flash Pack Forty)