|Rights campaigners say the controversial law encourages religious extremism and persecution of minorities [AFP]
Strikes and rallies have been staged across Pakistan against proposed changes to the country's blasphemy laws.
Protests were staged in Islamabad, Lahore, Peshawar, Quetta and Karachi against a move to amend a law which permits death sentences for those found to have committed blasphemy.
The law received attention in November when Asia Bibi, a Pakistani Christian woman, was sentenced to death after being found guilty of defaming the Prophet Muhammad.
Pope Benedict XVI has called for the release of Bibi, a mother-of-five, who is now in jail pending an appeal.
Human rights campaigners say the existing law encourages Islamic extremism.
Demonstrations turned violent in Karachi as angry protesters clashed with police in the southern port city.
Police said they used tear gas against demonstrators who had pelted officers with stones and shouted slogans, including "we will sacrifice our lives, we will save the sanctity of the Prophet".
Conservative religious groups had called for a national strike, which went ahead despite an announcement on Thursday from Samsam Bokhari, the deputy information minister, that the government had no intention of amending the law.
"We will start a civil disobedience movement if the government makes any amendment to the law," Sahebzada Fazal Karim, the chairman of the influential Muslim grouping the Sunni Ittehad Council, told the AFP news agency.
Naseer Tanoli, a police official, said a group of 100 protesters in Karachi were to join a main rally elsewhere in the city, but wished to march past the home of Asif Ali Zardari, the president, en route.
"We asked them to use a different route we had assigned for it. But they refused and pelted stones on the police, which forced us to use tear gas," Tanoli said.
Around 5,000 people rallied in the city, carrying placards and banners inscribed with anti-government and anti-US slogans. Some chanted "Death to America!"
Irshad Bokhari, the president of Karachi's local transport association, told the AFP news agency that public transport would remain off the road as part of the strike.
Atiq Mir, chairman of the All Karachi Traders Unity, said: "All markets and business centres are closed because the protection of Prophet Muhammad's honour is supreme to us."
More than 2,500 activists from different religious parties held three protest rallies in Multan city in central Punjab province, where a shutter-down strike was observed and markets and bazaars were closed.
Hundreds of protesters rallied in other main cities of northwestern Khyber Pakhtunkhwa and southern Baluchistan provinces.
In the eastern city of Lahore, about 1,500 people participated in four separate protest demonstrations.
Only around three per cent of Pakistan's population of 167 million are thought to be non-Muslim, and minorities complain of discrimination.
Pakistan has yet to execute anyone for blasphemy. Most of those given the death penalty have their sentences overturned or commuted on appeal through the courts.