U.S. Central Command chief General James Mattis has said that it was "no surprise" that there may be some relationship between Pakistan's Inter-Services Intelligence (ISI) and the Taliban, but he said the motives were unclear to him.

"I think though that it's hard to wipe the slate clean and just start over at any one point. Clearly the offensive against many of the people they allegedly used to work with has shown they are no longer friends with most of them," The Daily Times quoted Mattis, as having told the Senate Armed Services Committee.

He however said that the US' cooperation with Pakistan on counter-terrorism operations is at an "all-time high".

"I think we have a stronger strategic relationship... It is in the right direction," Mattis said.

Mattis also reiterated the Obama administration's demand and said that top leaders of the Quetta Shura and the Haqqani network must designated as terrorists.

"Both those groups have engaged in terrorism, and I believe the leaders of both groups should be placed on the State Department list," Mattis said. (ANI)