Three Indian soldiers and a woman were killed when militants ambushed a patrol in South Kashmir early on Thursday, part of an upsurge of violence that has hit the restive northern region as it emerges from winter.

An army and police party was returning from a village in the Shopian district of South Kashmir when it came under attack. Four soldiers were wounded in the one-hour firefight, according to police and witnesses.

"Around 2 in the night (2030 GMT), we woke up after hearing firing on the road," the son of the woman told Reuters Television.

"Our mother was sleeping upstairs. The firing stopped after an hour and when we went upstairs, we found our mother dead."

Television footage showed grieving relatives; a red van with shattered windows and shards of glass on the front seat; pools of blood on the ground and bullet marks on the walls of buildings.

A search was under way for the assailants in the latest in an upsurge of militant violence since Feb. 12 that has killed eight soldiers, eight gunmen and three civilians in the part of Kashmir that is controlled by India.

India is trying to contain a separatist insurgency in its northernmost region that is more than a quarter-century old. Protests flared after security forces killed a popular militant leader called Burhan Wani last July.

India launched what it called "surgical strikes" along the de facto border with Pakistan after an attack last September on an army base it said was carried out by separatist infiltrators. Pakistan denies any role in the attacks.

The nuclear-armed neighbours have fought two of their three wars since independence over Kashmir, which each claims in full but rules only in part.