Ethnic Rakhine rebels killed 13 Myanmar police officers Friday in a coordinated attack on the country’s Independence Day, according to the army.

Rakhine state has seen a surge in violence in recent weeks between the Arakan Army (AA) rebels – who are demanding greater autonomy for their Buddhist ethnic group – and security forces, displacing thousands.

It has added a fresh layer of complexity and danger to the violence in an area already scored by deep ethnic and religious enmity, which saw hundreds of thousands of Rohingya Muslims forced over the border by a brutal army crackdown in 2017.

Around 350 Arakan Army fighters descended on four police stations in northern Rakhine state early on Friday, “killing 13 police and wounding nine others,” according to a statement released late Friday by the army chief’s office.

The militants seized dozens of weapons and a quantity of ammunition before army reinforcements retaliated with two attack helicopters and infantry columns, added the statement, which was shared on a Russian social networking site.

“Strong action will be taken against the AA insurgents by security forces as they are making things more unstable and complicated in Rakhine,” it said.

In a Facebook post late Friday, the AA said three of its fighters “had been killed and some were injured” by Myanmar forces.

Myanmar marked its Independence Day on Friday – a highly-symbolic celebration of the declaration of freedom from British colonial rule in 1948.

But the country has since been fragmented by endless ethnic conflicts in its borderlands.

The AA told AFP that it had carried out the raids, blaming the military for using the police stations as a base from which to fire heavy artillery.

“The army brought the police into the war two weeks ago,” AA spokesman Khine Thukha said by phone, adding that the group had been under fire the whole day from army helicopters.

The AA later said “14 prisoners of war” taken in the clashes had been freed.

The UN’s humanitarian agency said Thursday it was concerned for the estimated 2,500 people currently displaced, many of whom are sheltering in local monasteries.

– with reporting by Agence France-Presse