Stones rained down and vehicles were set on fire as hundreds of protesters marched on the gates of the camp in protest against a Koran-burning incident at a US base earlier this week.
Without warning, a hand grenade was thrown, leaving a Norwegian solider with shrapnel wounds.
“He’s being treated at the hospital inside the base,” said army spokesman John Espen Lien
The soldiers fired warning shots and used tear gas and shock grenades to keep the demonstrators at bay.
It took four hours for the ISAF forces, aided by Afghan soldiers and police, to bring the situation under control.
Some 700 soldiers, half of them Norwegian, are stationed at the Maymana base. The remaining soldiers are from the United States, Latvia, Macedonia and Iceland.
John Espen Lien said the ISAF troops were expecting further turbulence on Friday.
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At least 14 people have died in the past two days in clashes in Afghanistan over the Koran burnings.
Taliban forces on Thursday urged Afghans to kill foreign soldiers in retaliation for the incident.