Afghan President Hamid Karzai said Saturday Afghanistan will not sign a strategic partnership deal with the US until NATO-led night raids and house searches stop.

The president's remarks came after he heard back from a government-appointed delegation assigned to look into civilian casualties sustained during recent NATO airstrikes and night time raids.

"The president stressed that the strategic partnership document will not be signed until the night raids and house searches stop," his office said in a statement.

"After hearing the report by the delegation, the president said that the arbitrary operations and house searches by NATO have become a serious problem between Afghanistan and NATO forces and that this has been one of the main obstacles on signing the strategic partnership deal with the United States."

The strategic partnership document being negotiated with Washington will govern the relationship between American troops and the Afghan government after the scheduled withdrawal of combat troops in 2014.

Night raids have been a persistent sticking point, but Karzai's refusal to sign until the operations end is his bluntest yet.

NATO has defended the operations as the safest way of targeting insurgent leaders, insisting they will continue but with the increasing involvement of Afghan special forces.

It insists that in 85 percent of night raids no shot is fired and they cause less than one percent of civilian casualties.

But Karzai has led public criticism of the controversial raids, saying they endanger lives and harass local communities, and repeatedly called on US-led international forces to stop entering Afghan homes.

The delegation appointed by Karzai investigated NATO airstrikes in Kandahar and Kapisa provinces in which several civilians died, and also a raid in Paktia in which the pregnant wife of the provincial anti-drugs chief was killed.

Lead investigator Mohammad Tahir Safi said: "We want civilian casualties to stop. We cannot tolerate any more.

"NATO-led ISAF forces have killed Afghan civilians for no reason."

According to the United Nations, the number of civilians killed in violence in Afghanistan rose by 15 percent in the first six months of this year to 1,462, with insurgents blamed for 80 percent of the killings.

There are around 140,000 international troops in Afghanistan fighting a decade-long Taliban insurgency alongside Afghan government forces.