At least 26 people were killed and 17 others wounded when gunmen opened fire on tourists in Indian-controlled Kashmir, the worst assault in years targeting civilians in a restive region that has seen an anti-India rebellion for more than three decades.

India's Prime Minister Narendra Modi says the gunmen behind a terrorist attack on tourists in the Kashmir region "will not be spared!"

India blames Pakistan for the attack in which 26 people, mostly Indian tourists, were killed in a scenic area popular with visitors, but Islamabad has denied involvement and a previously unknown militant group has claimed responsibility.