The attack in Nahri Sarraj district of Helmand province is another example of expanding violence in Afghanistan, especially in the Taliban´s heartland in the south.
The US is sending thousands of new troops to counter resurgent Taliban militants, who have made a comeback following their initial defeat by U.S.-led forces in 2001.
The Interior Ministry said the police checkpoint was attacked by "enemies of Afghanistan," a common reference to Taliban militants.
Lightly-armed police bear the brunt of militant attacks across the country, and their training is part of measures the U.S. and other international partners have identified as key to battling the insurgency.
The attack came a day before President Barack Obama is expected to announce the results of his administration´s review of U.S. policy in Afghanistan and Pakistan, which is also embroiled in an insurgency.
US-led forces toppled the Taliban government in Afghanistan in 2001, but many of them fled south and east into Pakistan. With the help of bases inside Pakistan, the Taliban has staged a violent comeback, especially in the last three years.
US and Afghan intelligence officials have said they suspect rogue elements in Pakistan intelligence agency of providing key information to the Taliban.
The New York Times carried a report on its website late Wednesday saying the assistance could go further than providing information.
The newspaper, citing American, Pakistani and other security officials who spoke anonymously because they were discussing intelligence information that they are not supposed to make public, said the widening Taliban campaign in southern Afghanistan is made possible in part by direct support from operatives in Pakistan´s military intelligence agency, the Directorate for Inter-Services Intelligence.
The Times said the support consisted of money, military supplies and strategic planning guidance to Taliban commanders. American officials said proof of the ties came from electronic surveillance and trusted informants, the report said.
The Pakistani officials said they had firsthand knowledge of the connections, though they denied that the ties were strengthening the insurgency. The newspaper said the Pakistani Embassy in Washington declined to comment.
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