At least seven security personnel have been killed and five injured after gunmen opened fire on an army campsite in central Pakistan, officials say.

The attack happened at a site along the Chenab river in the Gujrat district of central Punjab province.

The camp had been set up to search for the body of an army pilot whose helicopter crashed in May.

Security targets in Pakistan's north-west are frequently hit, but analysts say attacks in this area are unusual.

No group has said it carried out the attack as yet. Reports said the attackers opened fire on the troops from a bridge

"The exact number of attackers is not known but they came by motorbike and sprayed bullets on the troops from the bridge," a senior security official told the AFP news agency on condition of anonymity.

The attack took place hours after a rally nearby of hardline jihadist groups protesting against Pakistan's reopening of Nato supply routes to Afghanistan.

Officials say they are investigating whether the two events were linked.