Recommendations to interrogators at Guantanamo Bay rank the Inter-Services Intelligence Directorate alongside al-Qaida, Hamas and Hezbollah in Lebanon as threats, ''The Guardian'' reported quoting secret US files obtained by it.
"Being linked to any of these groups is an indication of terrorist or insurgent activity," the documents dated September 2007 said.
"Through associations with these...organisations, a detainee may have provided support to al-Qaeda or the Taliban, or engaged in hostilities against US or coalition forces (in Afghanistan)," the document said.
A New York Times report quoted a document as saying that detainees associated with the ISI and the militant groups "may have provided support to al-Qaida or the Taliban, or engaged in hostilities against US or Coalition forces".
The document provides "indicators" to officials to determine a "detainee''s capabilities and intentions to pose a terrorist threat if the detainee were given an opportunity".
It lists 36 groups and organisations as "terrorist and terrorist support entities".
Besides LeT, blamed for Mumbai attacks, JeM and Harkar ul-Jihad, which have carried out blasts in India, other Pakistan-based groups in the list are Ansar al-Islam, Harkat ul-Mujahideen (HuM) and the Markaz Dawah al-Irshad, the erstwhile political wing of the LeT.
There was no official word from Pakistani authorities on the development.
The revelation has come at a time when ties between the US and Pakistan and their spy agencies have been strained by several incidents.
The relations plunged to a new low after CIA contractor Raymond Davis gunned down two Pakistani men in Lahore in January.
Davis was freed after over two million dollars was paid to the families of the dead men in March but ties took a turn for the worse due to Pakistan's angry opposition to a US drone strike carried out a day after Davis' release that killed over 40 people.
The fresh revelation on ISI links with terror groups, The Guardian said, comes on the heels of its own "published evidence" that US intelligence services had been receiving reports of ISI support for the Taliban in Afghanistan for many years.