The gunmen riding on a motorcycle opened fire on the military police vehicle while it was passing through the Tibet centre area on the congested M A Jinnah road yesterday.
Two security personnel who were in the car were critically injured and rushed to a hospital where they died of injuries.
Ali bin Suffian, a purported spokesman of Lashkar-e-Jhangvi al-Alami, in an email took responsibility of the attack.
"While claiming responsibility of Karachi attack, we warn the government to immediately stop the killing of our companions in fake encounters, otherwise it should be ready for more deadly attacks," he said.
The group is linked with anti-Shiite Lashkar-e-Jhangvi (LJ) group responsible for several tragic attacks at the Shiite Muslims in the country.
LJ chief Malik Ishaq and his two sons were killed along with 11 other militants by police in Punjab in July in a shootout which many consider as a staged encounter.