NATO 'Regrets' Air Strike Deaths
Nato has said it "strongly regret[s] the loss of life" after a "friendly fire" attack on rebel tanks in eastern Libya which left at least four dead.
Earlier, a Nato commander had refused to apologise, saying that until Thursday's strike, the alliance had not been aware the rebels had tanks.
UK Foreign Secretary William Hague said "mistakes do happen", but Nato should be ready to say sorry for the deaths.
Rebel forces reacted with anger at the attack on their tanks near Ajdabiya.
However, rebel commanders stressed it would not damage relations with the allied force.
On Friday, Mr Rasmussen described the situation on the ground as "fluid", saying: "We have seen in the past that tanks have been used by the Gaddafi regime to attack civilians."
He went on: "This is also the reason why our aircraft target military equipment that could be used to attack civilians, but I can assure you that we do our utmost to avoid civilian casualties."
Earlier on Friday, Rear Adm Harding said: "I'm not apologising."
He said government tanks known to have previously targeted civilians in the western city of Misrata had been on the road on Thursday. At that point, Nato did not know that rebel troops had begun to bring out their tanks.
"Up until yesterday, we had no information that the... opposition forces were using tanks," he told reporters in Naples, near the Nato base which is co-ordinating the Libya operation.