The killing of Jawad Hussain Jawadi sparked violent protests by angry Shi'ites in the town of Dera Ismail Khan 280 (175 miles) southwest of the capital, Islamabad. Jawadi was leader of a Shi'ite youth group in the town and an active member of the community.
The attackers opened fire as he was walking near a town market, killing him on the spot, police said.
''We have no details except that there were two attackers riding a motorbike,'' said senior police officer Aslam Khan.
Thousands of people have been killed in sectarian attacks by Sunni and Shi'ite militants in Pakistan since the 1980s. Shi'ites make up about 15 percent of the mostly Sunni Muslim country's population.
As news of Jawadi's killing spread, several groups of protesters roamed the town, throwing stones at shops and blocking roads with burning tyres, police and witnesses said.
''They're angry and chanting slogans against the government and local administration,'' said resident Shaukat Khan.
No casualties were reported and police said the situation was under control.
Separately, authorities have identified a man killed after he launched a gun and grenade attack at Islamabad airport on February 6, news reports said.
Three security men were wounded in the attack. The man, initially described as a suicide bomber, was killed when one of his grenades went off. It was not clear if it went off accidently.
Authorities published a picture of the man in a newspaper on Wednesday, appealing for help in identifying him.
Geo Television said the man had been identified as a resident of a central town who had links with a banned Islamist group and had disappeared from his home six months ago.
REUTERS KD ND1512