Buddhist Rakhine fighters have killed 13 policemen and injured nine in attacks on police posts in Myanmar's troubled Rakhine State, the official news agency said.

The official Myanmar News Agency said four police posts in the Buthidaung area in northern Rakhine came under attack from hundreds of Arakan Army (AA) fighters after daybreak on Friday.

The western state has been torn by violence once again since early December, when fighting intensified between government forces and the AA, which wants more autonomy for the Buddhist Rakhine ethnic minority.

Rakhine State was where a brutal military-led crackdown in 2017 drove hundreds of thousands of the mostly Muslim Rohingya into bordering Bangladesh.

The recent fighting with the AA forced 2,500 civilians to flee their homes by the end of last year, according to the United Nations.

Khine Thu Kha, spokesman for the rebels, told the AFP news agency, that AA fighters retrieved seven corpses of "enemies" and took 14 members of the security forces captive during the raids.

He told Reuters later that the rebels had freed at least 12 members of the security forces it detained in the fighting.

Khine Thu Kha added that the attacks were a response to a Myanmar military offensive against the AA in recent weeks that also targeted civilians.

'Clearance operations'

Last month, the military announced a four-month halt in fighting in the north and northeast of the country to kick-start peace talks with multiple armed groups fighting for ethnic autonomy, but that announcement excluded Rakhine State.

The AA has said the army is using the truce elsewhere to focus efforts on Rakhine.

But observers say no major troop redeployments have yet taken place.

The escalation of violence comes amid a series of unclaimed attacks and murders in recent weeks in northern Rakhine.

Unknown assailants murdered a policeman, while two ethnic Rakhine were found with their throats slit, prompting the army to launch localised "clearance operations".

Zaw Min Tun, Myanmar military spokesman, told Reuters that Friday's attacks targeted police posts in the northern parts of Buthidaung and Maungdaw townships, a rugged area near the border with Bangladesh.

"The military will continue its operations in the area for security," he said, declining to confirm how many people were killed and captured by the armed group.

Zaw Min Tun said the attacks began minutes after the national flag was raised across Myanmar to mark 71 years since independence from Britain.

The AA's Khine Thu Kha said the attacks were not intended to coincide with the anniversary.

"We are not independent yet. Today is not our independence day," he said, referring to the Rakhine who he said faced discrimination in Myanmar.