(CNN) Members of a Rohingya militant group allegedly massacred dozens of men, women and children, execution-style in Hindu villages in Myanmar's Rakhine State last year, according to a new Amnesty International report.
The Myanmar government has blamed the Arakan Rohingya Salvation Army (ARSA) for attacking border guards and sparking a violent crackdown which has seen hundreds of thousands of Rohingya Muslims flee Myanmar into neighboring Bangladesh since last year.
In mid-2017, ARSA fighters engaged in "scores of clashes with security forces," according to Amnesty. At the same time, ARSA committed "serious human rights abuses...including unlawful killings and abductions," the human rights group said.
"It's hard to ignore the sheer brutality of ARSA's actions, which have left an indelible impression on the survivors we've spoken to," said Tirana Hassan, Crisis Response Director at Amnesty International.
On August 25, 2017, ARSA militants attacked a Hindu village in northern Maungdaw Township, and rounded up some 69 men, women and children, the majority of whom were killed, "execution-style," according to survivors who spoke to Amnesty.
The same day, 46 members of a Hindu community in a nearby village disappeared. As many 99 people could have been killed, Amnesty claims.
"In this brutal and senseless act, members of ARSA captured scores of Hindu women, men, and children and terrorized them before slaughtering them outside their own villages. The perpetrators of this heinous crime must be held to account," said Tirana Hassan, Amnesty International's crisis response director.
ARSA was able to recruit some villagers to help carry out the attack, but the "overwhelming majority of Rohingya did not," Amnesty said in its report, which it based on interviews with survivors and photographic evidence of the scene analyzed by forensic anthropological expert.
Myanmar's government welcomed Amnesty's findings. Spokesman Zaw Htay said the government had "credible evidence of more terrorist attacks by ARSA," adding that the international community had "ignored" ARSA's activities.
He added that ARSA is "a terrorist organization" and "initiators of the conflict in Rahkine"
ARSA denied the allegations leveled by Amnesty International in a statement, calling them "unjustifiable and careless."
"We do not commit any form of attack against any innocent civilian regardless of their religious and ethnic origin," ARSA said.
Both of the purported incidents at the hands of ARSA happened on August 25 -- the day ARSA attacked members of the country's security forces.
Myanmar authorities responded to the attack on the Tatmadaw, as the military is known, with what it called a security operations targeting terrorists. But human rights advocates say security forces have indiscriminately targeted Rohingya in what the UN's top human rights official called a "textbook case of ethnic cleansing."
More than 680,000 have fled the violence into neighboring Bangladesh, bringing stories of summary killings, mass rape and horrific violence against the Rohingya altogether.
A UN official told CNN in March that she's convinced the Tatmadaw's actions in August "bear the hallmarks of genocide."
"It's hard to ignore the sheer brutality of ARSA's actions, which have left an indelible impression on the survivors we've spoken to. Accountability for these atrocities is every bit as crucial as it is for the crimes against humanity carried out by Myanmar's security forces in northern Rakhine State," said Hassan.
Burmese authorities deny allegations of human rights abuses by the military and continue to maintain that the military is going after terrorists.
In September, Burmese state media reported that Myanmar authorities believed ARSA was responsible for a massacre against the region's Hindu community. Police found 45 bodies in mass graves at the time, the state-run Global New Light of Myanmar reported.
Rohingya are not recognized as an official ethnicity by the Myanmar government, which denies them citizenship, effectively rendering them stateless.
The Myanmar government also does not use the term "Rohingya." It considers them illegal immigrants from neighboring Bangladesh due to their roots in East Bengal, despite the fact that many Rohingya families have lived in Rakhine State for decades.