Four Burmese soldiers were killed and one was injured on Tuesday when troops were attacked by suspected Muslim insurgents near the country’s border with Bangladesh, an official said.

The Burmese army, known as the Tatmadaw, has been sent into northern Arakan State to seek attackers who killed nine police officers guarding the border early on Sunday.

The majority of residents in the area are Muslims belonging to the stateless Rohingya ethnic group.

Around 2:30pm on Tuesday, soldiers came under attack close to Pyaung Pyit village in Maungdaw Township, said Ye Naing, a director at the Ministry of Information.

“One Tatmadaw soldier was injured and four were killed by the Muslim insurgents. One was dead on the enemy side,” Ye Naing told Reuters late on Tuesday.

“Two guns and two magazines of ammunition were found.”

Nine border police officers were killed and five were wounded in Sunday’s clashes, in which officials said scores of Rohingyas swarmed border guard posts and made off with guns and ammunition.

Soldiers and police have been scouring Maungdaw Township since Sunday, employing helicopters to search the rugged terrain close to the frontier, which has been closed.

In at least one instance, the hunt for suspects has led to soldiers killing residents who officials said ambushed them but who local Muslims said were trying to flee.

State media reported on Tuesday that four bodies were discovered after soldiers opened fire in Myothugyi village, also in Maungdaw Township.

Four suspected insurgents have been detained, said Ye Naing.

Police told Reuters earlier on Tuesday that two suspects had said during interrogation that Sunday’s attacks were coordinated by a single leader operating on both sides of the Burma-Bangladesh border.

The events marked a dramatic escalation in violence in Arakan State, which has seen bouts of conflict between Muslims and ethnic Arakanese Buddhists but has not typically been the site of armed insurgency.

[related]

Vijay Nambiar, special adviser on Burma to UN Secretary-General Ban Ki-moon, called on civilians in “the area to exercise maximum restraint and not be provoked into any kind of response by targeting other communities or religious groups.”

The Rohingya bore the brunt of intercommunal clashes that broke out in Arakan in 2012, in which more 100 people were killed. They make up most of the 125,000 people still living in displacement camps in Arakan State and face severe restrictions on their movements.

Burma‘s de facto leader, Aung San Suu Kyi, appointed former UN chief Kofi Annan in August to chair an advisory commission on issues in Arakan State.