The actions of Myanmar's military might constitute "crimes against humanity", Amnesty International says, amid widespread allegations of violence against Rohingya Muslims.
The rights group's latest report accuses Burmese forces of murdering civilians, rape, torture and looting.
Myanmar's military has denied accounts of atrocities against the minority group and says it is conducting anti-terrorist raids in Rakhine.
It comes as regional leaders gather in Yangon, hosted by the country's de-facto leader, Aung San Suu Kyi, to discuss the violence.
It is extremely rare for ASEAN, the 10-nation regional body representing South East Asia, to discuss the affairs of a member country.
Reports of violence in Rakhine State began in October, after the army launched an anti-insurgency operation.
The operation started after border police were attacked by a militant group, which Amnesty said was composed primarily of Rohingya.
In November a UN official said Myanmar was conducting "ethnic cleansing" of Rohingya, while Human Rights Watch has published satellite images of razed villages.
Amnesty said it interviewed 35 victims and 20 others involved in humanitarian and reporting efforts in Myanmar, also known as Burma.
It described a "humanitarian catastrophe" with random killings, arbitrary arrests and detentions, rapes, torture, looting and destruction of property including the torching of 1200 homes and other buildings like schools and mosques.
Amnesty said the army's actions were "part of a widespread and systematic attack against the Rohingya population in northern Rakhine State and may therefore constitute crimes against humanity".
It is unclear how many civilians have died in the latest conflict as the government has restricted journalists and aid workers from accessing the area.
Amnesty has estimated at least 27,000 Rohingya have fled to neighbouring Bangladesh since October, placing a strain on impoverished communities along the border. It also accused the Bangladeshi government of actively turning away refugees.
It called on the Burmese government and Ms Suu Kyi to order a stop to the violence, publicly condemn rights violations, allow unimpeded access to Rakhine and launch an impartial investigation with the UN.
The Myanmar government has invited an international advisory committee led by former UN secretary-general Kofi Annan to look into the situation.
Ms Suu Kyi, who is hosting the meeting in Yangon, defended her government's handling of the issue and accused the international community of stoking resentment.
Members of the Muslim Rohingya community are widely regarded as illegal migrants in majority-Buddhist Myanmar, and have experienced persecution for decades amid simmering ethnic tensions in Rakhine.
- BBC / RNZ