The ultras lobbed the explosive at the residence of state forest department ranger Konsam Achouba at interior Pourabi Mayai Leikai village yesterday but the grenade failed to explode.
Achouba and his family members were present at the time of the incident, they said, adding that no individual or group has claimed responsibility for the attack.
Family members of the official said a militant outfit had demanded a huge sum of money from the family about a month ago but they have not contacted the family after that.
A 9mm pistol along with some rounds of ammuntion and 'letters demanding money from the public' were allegedly recovered from the possession of the two.