Libyan rebels said Sunday they were closing in on Qaddafi’s main stronghold of Tripoli and a 600-strong unit is within 20 miles (30 kilometers) of the capital.

NATO spokesman Col. Roland Lavoie says he can’t confirm that because the situation on the ground had become so fluid in recent days that it’s difficult to track all developments.

He says much of the fighting now is concentrated in towns and villages, complicating the identification of targets. He says “there is no longer a traditional front line as we had in other phases of the conflict.”