Fighters from the Arakan Rohingya Salvation Army (ARSA) launched coordinated attacks against police posts in Myanmar's Rakhine state, and attempted to break into an army base.
Over 150 fighters were involved in the attack, which took place in the Maungdaw township at 1am on Friday.
Twelve members of the security forces were killed in the attacks, along side 77 Rohingya Muslims, who the government alleges were all fighters.
The ARSA, which was previously called Harakah al-Yaqin launched its first attack in October, warning that more attacks would take place. Rohingya Muslims have faced systematic persecution by the Myanmar government with credible allegations of security forces committing crimes against humanity.
The Myanmar army said in a statement: “In the early morning at 1am the extremist Bengali insurgents started their attack on the police post... with the man-made bombs and small weapons."
The UN has condemned the attack and called for “all parties to refrain from violence, protect civilians and restore order”.
“We are deeply concerned about the security situation in Rakhine state,” UN resident coordinator in Myanmar, Renata Lok-Dessallien said.