WASHINGTON - A top American general says that the United States is holding back $300 million in coalition support fund to Pakistan as it is not putting enough pressure on the Haqqani network.

“There is not adequate pressure being put on the Haqqanis" by the Pakistan government, General John Nicholson, the commander of US and NATO forces in Afghanistan told a news conference at the Pentagon on Friday.

He said this was the reason that the US Defence Secretary Ashton Carter was not giving the necessary certification to unblock the funds to Pakistan.

Relations between Islamabad and Washington have been frayed over the past decade because of US claims that Pakistan was unwilling to act against Haqqanis.

“The Haqqanis operationally have been able to continue to conduct operations inside Afghanistan. They constitute the primary threat to Americans, to coalition members and to Afghans, especially in and around Kabul,” the general added.

Though he acknowledged the number of attacks in the capital city has fallen to 16 this year compared to 23 during the same period in 2015, crediting joint US and Afghan security measures.

Pakistan denies the presence of any sanctuaries and insists counter-terrorism military operations have indiscriminately targeted and uprooted all militant infrastructures on their side of the border, including those of Afghan insurgents.

"As far the strength of the Haqqanis, the Secretary of Defence in August in his response to Congress as a result of the National Defence Act and Authorisation Act of 2015, he was required to respond to Congress on whether there was adequate pressure being placed on the Haqqanis by the Pakistan government," Gen Nicholson said.

"And he said he was unable to certify that there was sufficient pressure being placed on them to justify additional coalition support funds to Pakistan. Kind of a lengthy explanation, but it was his way of saying that there's not, not adequate pressure being put on the Haqqanis," Nicholson told reporters.

Nicholson said US troops in Afghanistan have been authorised by President Barack Obama to take any measures necessary to defend against the Haqqani threat."We have authorities into terms of force protection, so we can act against them when we identify them. We track their actions very closely. Especially as relates to the Kabul threat streams. I have the authorities I need to defend us against that threat," he said.

Nicholson also confirmed a brother of Sirajuddin Haqqani, the chief commander of the network, is in Afghan custody and has been sentenced to death by a local court.

But Nicholson indicated it may take a while before the high-profile trial is concluded, saying the death sentence is currently going through the appeals process.

“The trial and the subsequent appeal process is entirely in control of the Afghan government so that is up to them how this plays out… And the appeals process just began, so I would expect this to continue into 2017 because of the appeals process,” he said.

The Taliban have warned of “disastrous consequences” if the higher Afghan courts also uphold Anas Haqqani’s death sentence.

The Taliban have described the man as “an ordinary student of [a] religious school,” saying he is not involved in any political or military activity, nor has there been any prize money on his head. It also alleges the US military is behind Anas Haqqani’s arrest and the judicial verdict.