Earlier on Thursday, Pakistan's Express Tribune newspaper quoted senior security officials as saying that a formal announcement of the ban on the Haqqani network and 11 other militant organizations would be made in "coming days."
The Pakistani government did not respond when asked by Reuters to confirm the report.
In Washington, a spokeswoman for the US State Department said the United States welcomed reports of the planned ban.
"This is an important step towards eliminating terrorist activity in Pakistan," Marie Harf told a regular news briefing. She added that she was aware an announcement was planned, but did not know when this would happen.
Harf noted that US Secretary of State John Kerry had just visited Pakistan, where he had had "wide-ranging conversations with the Pakistanis about counter terrorism."
"Certainly he emphasized that we are committed to deepening our security partnership with Pakistan," she said.
If the government formally announces a ban on the powerful Haqqani network, which attacks targets in Afghanistan from its bases in Pakistan, it would show it was keen to convince to the United States that it is serious about pursuing the militants. However, it would remain to be seen whether this translated into significant action on the ground.
Pakistan has long been suspected by the West of playing a double game, fighting some militants while supporting those its generals have regarded as strategic assets to be used against rivals and neighbours, India and Afghanistan.
However, after a militant attack on a school in the city of Peshawar last month in which 134 children were killed, Pakistan promised to stop differentiating between "good" and "bad" militants and to step up operations against their hideouts on the Afghan border.
Kerry said in Pakistan on Tuesday that Pakistan must fight militant groups like the Haqqani network that threaten Afghan, Indian and US interests.
Pakistani foreign affairs adviser Sartaj Aziz told Kerry that action would be taken "without discrimination against all groups."
© Thomson Reuters 2015