A man has been found dead with stab wounds in Myanmar's Rakhine State, in what the government said on Monday was the second murder in under a week of a Rohingya who cooperated with authorities as they crack down on suspected insurgents.

Coordinated attacks on October 9 killed nine police officers and sparked a military operation in northern Rakhine. The government of predominantly Buddhist Myanmar blamed Muslim Rohingyas supported by foreign militants.

State media has reported at least 86 deaths and the United Nations says 34,000 people have fled to Bangladesh.

The violence poses a challenge to Aung San Suu Kyi's government and has renewed international criticism that the Nobel laureate has done too little to help the Rohingya, who are denied citizenship in Myanmar.

Residents and rights groups say soldiers have raped Rohingya women, burnt homes and killed civilians during the operation near the frontier with Bangladesh.

The government denies the accusations, and has launched a social media campaign in an effort to demonstrate that security forces are acting properly in Rakhine.

An administrator in Yae Twin Kyun village, named as Rawphi, was found dead with knife wounds on Sunday, Lieutenant Colonel Aung San Win of the local border guard police told Reuters.

He said the killing of the 28-year-old Muslim might be "related to terrorism".

Myanmar's state counsellor's office said on Monday evening on its Facebook page that the victim had been "cooperating with members of security forces in administration duties."

The case is the second murder in Rakhine where authorities have highlighted the victim's cooperation with the government, appearing to point the finger at Rohingya insurgents.

On Friday, the state counsellor's office said a Muslim man was decapitated after he had denied stories of Myanmar military abuse when speaking to reporters.

"He told media that there was no case of arson by the military and police forces, no rape and no unjust arrests," said a Facebook post accompanied by a picture of a headless body with English text that read: "truth teller beheaded".

Neither the police nor the state counsellor's office have said who was responsible for the decapitation.

A Rohingya community leader, who asked not to be named for fear of reprisals, told Reuters many Muslims were sceptical about the government's account of the beheading.

A report by the International Crisis Group said insurgents calling themselves Harakah al-Yaqin were responsible for the attacks on Oct. 9 that sparked the crackdown. The group also have killed Rohingyas who threatened to inform on them to authorities, the ICG said.

Reuters could not independently verify the government accounts as access for independent journalists to northern Rakhine has been prohibited since security forces locked down the area.