Barakzai said the post had been set up recently to protect convoys supplying Nato troops in Afghanistan.
Baghlan province lies on the route used by the Nato military alliance for supplies to its troops.
Claim of responsibility
A man claiming to speak for Hezb-e-Islami, an Afghan group, told the AFP news agency in a telephone call that his group had carried out the attack.
One of the group's fighters also died during the assault, he said.
Hezb-e-Islami is led by former Gulbuddin Hekmatyar, a former Afghan prime minister who is on the United States' most wanted list of "terror" suspects.
The attack underscores the vulnerability of Afghan police, whose training, along with that of the local military, is a priority in the recently announced US strategy for Afghanistan.
Barack Obama, the US president, this month gave the order for 30,000 more US troops to be deployed to Afghanistan.
The US government is aiming to begin withdrawing American troops in July 2011.