Haq Nawaz was hanged early on Wednesday morning at Mainwali jail in Punjab province for the killing 10 years ago of an Iranian diplomat.
Haq Nawaz was hanged early on Wednesday morning at Mainwali jail in Punjab province for the killing 10 years ago of an Iranian diplomat.
His body was later released to relatives for burial in the town of Jhang.
But a large crowd, waiting for the return of his body, clashed with police outside Nawaz's house. The police said they were forced to use bullets and tear gas to keep control.
One person was killed and six others were wounded - although members of Sepa-e-Sahaba said the number of wounded was higher.
Several hundred supporters of the militant group Nawaz belonged to, Sepa-e-Sahaba, had been taken into custody before the execution to prevent large-scale protests.
Sectarian killings
Security measures throughout Pakistan were tightened ahead of the hanging.
Nawaz was sentenced to death by an anti-terrorism court 10 years ago after being found guilty of shooting Sadiq Ganji, who was the Director of the Iranian Cultural Centre in the provincial capital, Lahore.
Mr Ganji was the first prominent Shi'a Muslim from Iran to be killed in violence between Shi'as and Sunnis which began around two decades ago and has so far resulted in around 1,000 deaths.
Since then, several Iranian Shi'as have been murdered in sectarian attacks that have been blamed on the hard-line Sunni Sepa-e-Sahaba organisation.
The violence has at times severely strained Islamabad's relations with Tehran.
Government clampdown
Mr Nawaz was one of the first Sepa-e-Sahaba members to face the gallows.
The government says that it is in a better position to clamp down on sectarian violence than its civilian predecessors, who it argues were often held to ransom by hard-line groups.
But the human rights organisation Amnesty International said in a news release that the death penalty would not resolve the violence.
"The use of the death penalty only encourages the cycle of violence to continue as sectarian groups seek revenge for those executed," it said.
Meanwhile, the sectarian violence which has dogged Pakistan for much of the last 10 years has continued unabated: in just over a week, seven people, six of them Shi'as, have been killed.