The Plan International aid worker shot by Myanmar security forces in Rakhine state was carrying a grenade according to the armed forces and has been charged under a counterterrorism law.

Myanmar national Ye Lin Naing, 25, was driving a motorcycle in Mrauk U township Sunday when "a security forces member opened fire... as a warning shot" when he did not stop, according to a statement from the commander-in-chief's office.

Rakhine state is one of Myanmar's poorest regions and NGOs provide aid to tens of thousands of Rohingya Muslims still languishing in displacement camps as well as other local communities.

But Myanmar's army has deployed thousands of troops there in recent months to try and crush the Arakan Army (AA), who are fighting for more autonomy for ethnic Rakhine Buddhists.

Plan International, a prominent aid agency that provides aid to displaced households and children affected by conflict in Rakhine, said it was "extremely concerned" about their employee who remains in the custody of security forces.

Additional reporting AFP