Drone strikes and other "targeted killings" of terrorist and insurgent leaders favoured by the US and supported by Australia can strengthen extremist groups and be counterproductive, according to a secret CIA report published by WikiLeaks.

According to a leaked document by the CIA's Directorate of Intelligence, "high value targeting" (HVT) involving air strikes and special forces operations against insurgent leaders can be effective, but can also havenegative effects including increasing violence and greater popular support for extremist groups.

An MQ-1 drone flies over California. Drones have killed up to 3888 people in 10 years. Credit:Reuters/US Air Force

The leaked document is classified secret and "NoForn" (meaning not to be distributed to non-US nationals) and reviews attacks by the United States and other countries engaged in counter-insurgency operations over the past 50 years.

The CIA assessment is the first leaked secret intelligence document published by WikiLeaks since 2011. Led by Australian publisher Julian Assange, the anti-secrecy group says the CIA assessment is the first in what will be a new series of leaked documents relating to the US agency.