A bomb exploded near a Pakistani paramilitary complex in the southern port city of Karachi late Wednesday killing three soldiers and wounding four others, officials said.
"It was a bomb blast, the target seems to be a van of carrying soldiers," police official Karim Khan told AFP.
The blast happened near the Rangers' headquarters in the city's eastern district of Korangi, he added.
Police cordoned off the area and ambulances rushed the casualties to the state-run Jinnah Hospital.
"We received seven wounded soldiers, three of them expired later," senior doctor Seemi Jamali said, adding that two were in critical condition.
"It was an attack on the Rangers' pickup truck," senior police officer Tahir Naveed confirmed. "An explosive device, most probably a hand grenade was hurled into the moving van causing the casualties," Naveed told AFP.
The attack might be linked to operations being carried out by Rangers against militants and criminals gangs in the city, he added.
Recent violence in Karachi and elsewhere has fuelled fears of instability as the country heads towards general elections in May.
The city of 18 million, which is Pakistan's business hub, last year saw around 2,000 people killed in violence linked to ethnic and political tensions, its deadliest toll in two decades.