WASHINGTON - In a potential blow to US-Pakistan relations, the Pentagon has withheld $300 million in military reimbursements to Pakistan, amid claims by American officials and lawmakers that Islamabad was unwilling to act against militant groups such as the Haqqani network.

Adam Stump, a Pentagon spokesman, said that Defence Secretary Ashton Carter had decided against making a certification to Congress stating that Pakistan is taking sufficient action against the Haqqani network, a Taliban affiliate blamed for attacks on US and allied personnel in Afghanistan.

“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,” the spokesman said.

The $300 million comes under the Coalition Support Fund (CSF), a US Defence Department programme to reimburse allies that have incurred costs in supporting counter-terrorist and counter-insurgency operations. Pakistan is the largest recipient.

“This decision does not reduce the significance of the sacrifices that the Pakistani military has undertaken over the last two years,” Stump added.

Pakistan has been reimbursed $700 million of the $1 billion they were authorised in fiscal year 2015 under the CSF.

According to Pentagon data, about $14 billion has already been paid to Pakistan under the CSF since 2002. The decision by the Pentagon is a sign that while it sees some progress by Pakistan in its military operations in North Waziristan, much work remains.

Nadeem Hotiana, a spokesman for the Pakistani Embassy in Washington, said the CSF programme had allowed the United States to support Pakistani military actions, particularly in the country’s tribal areas, that had benefited both countries. “Pakistan will continue to work with its partners in a long-term effort for ensuring security and stability in these areas,” he said.

“Over the past decade, Pakistan has conducted a large number of military operations that have sequentially dismantled and destroyed terrorist infrastructure on its side on the international border with Afghanistan,” Hotiana said.

The latest of these major operations, known as ‘Operation Zarb-e-Azb’, has been a resounding success and it has cleared North Waziristan - the last bastion of militant networks - from terrorists of all affiliations. This decade-long effort in Pakistan has caused 60,000 fatalities, including 6,000 security forces personnel involved in the operations.

“Pakistan will continue its fight against terrorism and ensure that areas cleared by the security forces do not slide back into the control of terrorist networks,” Hotiana said.

The decision by Secretary Carter, an avowed India supporter, comes as the US grapples with deteriorating security in Afghanistan, where a resurgence in Taliban activity has derailed plans to definitively end the long military effort there.

It is the first time the Pentagon has withheld military aid to Pakistan because of the Haqqani group, and the decision was announced as Prime Minister Nawaz Sharif was presiding over a conference of Pakistani envoys in key countries in Islamabad.

Here is how Carter assessed US relations with India and Pakistan ahead of his recent visit to New Delhi: “We are long past the point in US policy-making where we look at the India-Pakistan dyad as the whole story for either one of them. We have much more to do with India today than has to do with Pakistan,” Carter had said. “There is important business with respect to Pakistan, but we have much more, a whole global agenda with India, agenda that covers all kinds of issues.

“With respect to Pakistan totally different. We have a big set of issues having to do with the border with Afghanistan where we continue to operate, with terrorism, both on the territory of Pakistan and also obviously cross-border into Afghanistan, including affecting US service members there,” Carter added.

Shamila Chaudhary, a former White House official of Pakistani origin and senior fellow at New America, a Washington think tank, was quoted as saying that the decision could foreshadow additional steps increasing pressure on Pakistan to crack down on militants causing trouble in Afghanistan.

“It is a way of sending a signal to the Pakistani military of what’s to come, in the sense that the United States is no longer willing to give blank checks to Pakistan,” she said.

Washington’s ties with Pakistan grew particularly strained after the United States secretly launched the raid that killed Al-Qaeda leader Osama bin Laden in 2011. Later that year, the Obama administration temporarily suspended $800 million in security aid.

Although tensions have eased since then, a stark reminder of the reasons for bilateral friction came this May, when a US drone killed Taliban leader Akhtar Mohammad Mansour on Pakistani soil. Pakistan, which has been the target of repeated militant attacks, has denied support for extremist groups.

Seeking to increase pressure on Pakistan, Congress introduced new requirements related to the Haqqani network in annual defence legislation beginning in fiscal 2015. Earlier this year, lawmakers also blocked Pakistan from using another pool of US military aid to buy American F-16 jets.