The Pentagon has withheld $300 million in military assistance to Pakistan, U.S. officials said Wednesday, a potential blow to U.S.-Pakistani ties and a sign of ongoing frustration with Islamabad for not acting against militants fueling violence in Afghanistan. This comes after US secretary of defense Ash Carter decided not to tell Congress that Pakistan was taking adequate action against the Haqqani network, a US official said. "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 on Wednesday.

The move ends a year of speculation about an aid program that has been fundamental to Pakistani military operations, and reveals the strains in Washington’s relations with an ally that many officials have accused of double-dealing with militant groups. The decision comes as the Obama administration grapples with deteriorating security in Afghanistan, where aresurgence in Taliban activity has derailed plans to definitively end the long military effort there. According to Pentagon data, about $14 billion has already been paid to Pakistan under the CSF since 2002.