The head of security, Asadullah Sherzad, in Helmand Province said the bomb exploded under the men's vehicle about 20 kilometers south of the provincial capital, Lashkargar.
The attack is the latest in a series of violent incidents in Helmand. On March 3, police in the province killed eight Taliban fighters and arrested 10.
Helmand Province Governor Comments
U.S. Marines operating in Helmand Province in 2002 (epa)
RULING A RESTIVE LAND: On February 12, RFE/RL Radio Free Afghanistan correspondent Jawaid Wafa spoke briefly with Helmand Province Governor MOHAMMAD DAOUD about the ongoing violence in his restive region on the border with Pakistan.
RFE/RL: Recently, there have been many clashes and attacks by insurgents in Helmand Province. What in your view facilitates these attacks, especially in Helmand?
Mohammad Daoud: This province has a 160-kilometer border with Pakistan's Baluchistan Province. In reality, armed people, armed terrorists, from the other side of the border cross the border into Helmand. They carry out attacks and return back. It is a serious problem in Helmand that within our borders there is neither tribal good will, nor are there are special military or security measures to prevent enemies from crossing back and forth.
RFE/RL: The attacks and clashes have not only been between government forces and insurgents. There have been various clashes in different parts of Helmand between police and purported drug smugglers. How do you explain this?
Daoud: Drug smugglers also use the border for their own purposes. They have opened markets on the border and process opium there. This is a serious problem along our border. We are in touch with our authorities on this problem.
RFE/RL: There are government border police patrol your border. What is their role in preventing illegal crossings?
Daoud: Along this 160-kilometer border, there are car routes, walking routes. We have border police, but unfortunately, either because of their own problems or because of weak administration, they have not been able to stop the crossing.