Casualty, if any, was not known, they said.
The insurgents fired at the security personnel of the 24th Assam Rifles battalion in the interior hill area, about 100 km from here, yesterday.
The security personnel retaliated and the exchange of fire lasted for several hours.
A spokesman of the banned Revolutionary People's Front (RPF) identified as Taohang Heiremcha said the ambush was carried out by cadre of its armed wing, People's Liberation Army (PLA).
In a statement, the spokesman claimed that at least three Assam Rifles personnel were injured.