A new US report asserted that Pakistan is not doing enough to fight against terror groups in its restive tribal belt.

"The Pakistan military continued to avoid military engagements that would put it in direct conflict with Afghan Taliban or al-Qaeda forces in North Waziristan," the 'Wall Street Journal' reported citing the 27-page White House report which is to be given to Congress.

The declassified report seen by the Journal also expressed concern about Pakistan's refusal to send more troops to the lawless tribal area, which is believed to be hiding some of the most wanted insurgents who are attacking American troops in Pakistan.

"This is as much a political choice as it is a reflection of an under-resourced military prioritising its targets," the report said.

The White House report could strain relations between the two allies and also cause Congress to cutback on billions of dollars of aid, according to the paper.

In South Waziristan, the report noted that Pakistan is unable to stabilise area after clearing it of militants, which leads to operations advancing slowly.

There, "the military largely stayed close to the roads and did not engage against those (Pakistani Taliban) militants who returned after fleeing into North Waziristan," it said.