Washington (CNN) The United States won't pay $300 million in military reimbursements to Pakistan after the Pentagon determined the country was not taking sufficient action against a US-designated terror group.

"The funds could not be released to the government of Pakistan at this time because the Secretary has not yet certified that Pakistan has taken sufficient action against the Haqqani network," Pentagon spokesman Adam Stump said in a statement, referring to Defense Secretary Ash Carter.

At issue are monies from the Coalition Support Fund (CSF) that the United States provides to countries to offset the costs they encounter for supporting counterterrorism operations. Pakistan has been the largest recipient of that aid.

Pakistan has received roughly $14 billion in reimbursements from the fund since 2002, according to the Defense Department.

"This decision does not reduce the significance of the sacrifices that the Pakistani military has undertaken over the last two years," Stump said, while adding the Pentagon continues to be "encouraged" by the actions of the Pakistani military in the country's tribal regions.

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