Three Pakistani soldiers were killed and four others wounded when a roadside bomb exploded near their vehicle in the country's biggest city Karachi on Friday, police said.
"Three troops from Pakistan rangers were killed and four were hurt, it was a remote control bomb," Sharfuddin Memon, a spokesman for the home ministry in the southern province of Sindh, said.
Officials said the rangers' vehicle was targeted in the eastern part of the city, which is the provincial capital of Sindh.
The attack was not immediately claimed by any group.
Nearly 4,700 people have been killed across Pakistan in attacks blamed on Taliban and other al Qaeda linked networks since government troops stormed a radical mosque in Islamabad in 2007.
Pakistan's economic hub, Karachi has also recently faced its worst ethnic- and politically-linked unrest in 16 years, with more than 100 people killed in one week alone in October.
The gang wars have been linked to ethnic tensions between the Mohajirs, the Urdu-speaking majority represented by the Muttahida Qaumi Movement (MQM), and Pashtun migrants affiliated to the rival Awami National Party (ANP).
The Pakistan rangers are part of the country's paramilitary forces, which are helping police try to maintain peace in the city.