BBC: The head of US forces in Iraq, Lt Gen David Petraeus, has told the BBC that fighting the insurgency is a "long term endeavour" which could take decades.
Speaking to the BBC's John Simpson in Baquba, Gen Petraeus said there was evidence that the recent troops surge was producing gains on the ground.
But he warned that US forces were engaged in a "tough fight" which will get "harder before it gets easier".
His comments come as US calls for a rapid troop withdrawal gather strength. US Iraq chief warns of long war (more)
Mark Alexander
