A day before the arrival of the President in Srinagar, militants attacked a passing army convoy in the north Kashmir Sopore town on Thursday morning.
A senior police officer said militants lobbed a grenade at a passing army convoy in Sopore town near the police station.
"The grenade missed the convoy and exploded on the road injuring 15 civilians, six of whom have sustained critical splinter injuries," said the officer.
The injured were taken to a local hospital where attending doctors referred six seriously injured persons to Srinagar for specialised treatment.
President A P J Abdul Kalam will arrive in Srinagar on Friday on a three-day visit during which he is scheduled to address a joint session of the state legislature.
President Kalam will also inaugurate a jurist conference being held in Srinagar in connection with the diamond jubilee celebration of the Jammu and Kashmir high court.
The authorities in Srinagar are on a maximum alert on the eve of the visit.