Suspected rebels using guns and grenades sneaked into a crucial army base in Indian-controlled Kashmir early Sunday and killed at least 17 soldiers in the deadliest attack on a military base in the disputed Himalayan region in recent years, the army said.

Four rebels were killed as the soldiers returned gunfire to the attackers in the surprise assault before dawn on the base close to the highly militarized Line of Control dividing Kashmir between India and Pakistan.

Indian Prime Minister Narendra Modi vowed to punish those behind the "cowardly" and "despicable" hours-long attack that also left four militants dead and scores of soldiers injured.