Police reinforcements have been called in the Pakistani city of Faisalabad a day after two Christians charged with blasphemy were shot dead outside court.
Clashes broke out in the city, home to a large Christian community, after the brothers were gunned down.
Pastor Rashid Emmanuel, 32, and Sajid, 24, were accused of writing a pamphlet critical of the Prophet Muhammad; a rights activist said they were framed.
Pakistan's controversial blasphemy law carries the death penalty.
A police officer who was escorting the brothers from a district court on Monday was critically wounded when the unidentified gunmen opened fire and then escaped.
At least 10 people were reportedly injured as stone-throwing and rioting broke out in a Christian neighbourhood of the city afterwards.
Police reinforcements from nearby districts have been called in to restore order.
The brothers, from the Waris Pura area of Faisalabad, were arrested earlier this month.
The complainant in the case, a local trader, Khurram Shehzad, alleged that one of his employees was handed a pamphlet by someone at Faisalabad's general bus stand.
He said the paper contained disrespectful remarks about the Prophet Muhammad.
Police told the BBC the pamphlet had apparently been signed by the two brothers, whose addresses and mobile phone numbers were also given.
But Atif Jameel, spokesman for the Pakistan Minorities Democratic Foundation, told the BBC: "No-one in his right mind would issue a derogatory pamphlet against the Prophet and put his name and address on it.
"This appears to be a conspiracy against peace and religious harmony in Faisalabad."
Earlier this month, several hundred demonstrators marched to the Waris Pura slum, which is home to nearly 100,000 Christians, and demanded the death penalty for the two accused.
Although no-one has ever been executed under Pakistan's blasphemy law, about 10 accused have been murdered before the completion of their trial, according to a BBC Urdu correspondent in Lahore.
Dozens more are living in exile to avoid punishment under the legislation.
Human rights activists want the law repealed as they say it is often exploited by Islamist extremists or those harbouring personal grudges.