and paramilitary force members were deployed.
"The hanging of Afzal Guru is a declaration of war by India," said Hilal Ahmad War, leader of a separatist faction.
Thirty-six people including 23 policemen were injured in protests, said police spokesman Manoj Sheeri, with most of the violence in Guru's home district.
Authorities shut down internet services to try to stop news of the hanging and unrest spreading. The chief minister of Jammu and Kashmir state, Omar Abdullah, made a televised appeal for calm.
Scuffles also broke out in New Delhi between Hindu activists and demonstrators who gathered at a city-centre protest site to condemn the execution, a Reuters witness said.
Five militants stormed the parliament complex in New Delhi on Dec. 13, 2001, armed with grenades, guns and explosives, but security forces killed them before they could enter the main chamber. Ten other people, most of them security officers, were killed.
Guru said he never got a fair trial and his brother reiterated that on Saturday, adding that authorities had not warned the family of his execution.
"At least the government should have given the family a chance to meet him," said the brother, Ajaz Ahmad Guru. "He didn't get a fair trial. His wife is in deep shock."
India said the Pakistan-based Jaish-e-Mohammad militant group was responsible for the parliament attack. The group fights Indian rule in Muslim-majority Kashmir.
The hanging last year of Mohammad Ajmal Kasab, the lone surviving Pakistani militant involved in the 2008 Mumbai attacks, after a long lull in executions, prompted speculation that India would move quickly to execute Guru.
But unlike Kasab's execution, which sparked celebrations in the streets, Guru's case was seen as more divisive.
Some Kashmiri leaders warned that hanging Afzal would fuel the revolt in India's part of the Himalayan region in which tens of thousands of people have been killed since 1989.
Curfews were imposed in Srinagar, the region's summer capital in the Kashmir valley, and major towns including Baramulla, Guru's home town.
Kashmir is divided between India and Pakistan, both of which claim the region in full and rule it in part. They have fought two of their three wars over the region.