A local employee of the US embassy in Pakistan's capital Islamabad was shot dead by an unidentified gunman on Sunday, police said.
The motive for the shooting was unclear. Police said the victim was a member of a minority community and was working in the US Drug Enforcement Administration in the embassy.
Police identified the victim as Iqbal Baig, a resident of G-9/1 district in Islamabad, and told AFP the attacker used a pistol.
Baig was shot at 2 am outside his home as an unknown number of accomplices waited in a nearby parked car.
"One of the armed attackers opened fire on Iqbal Baig. One bullet hit him on the left side in the chest and exited on the right side," Khalid Mehmood Awan, a senior police official at the scene, told AFP.
"Iqbal Baig was working in the US Drug Enforcement Administration for 12 to 13 years and was from the Ismaili Shiite sect. His brother told us that he has received threats in the recent past," Awan added, without detailing the nature of the threats.
The attackers, who fired shots in the air after the attack, managed to flee.
"We have collected some evidence from the site including a 9mm pistol in the nearby area," Awan added.
He said police were investigating several possible motives, including attempted robbery, sectarian killing and extremism.
No militant group has claimed the attack. No one at the US embassy in Islamabad was immediately available for comment.
Sectarian violence - in particular by Sunni Muslim hardliners against Shiite Muslims who make up roughly 20 percent of Pakistan's 200 million people -- has claimed thousands of lives in the country over the past decade.
Forty-five Shiite Ismailis were killed in the southern city of Karachi in May in the first attack in the country claimed by Daesh.
The worst atrocities, however, have been in the southwestern province of Baluchistan, home to some 200,000 Shiites.