Responding to a question about the message at a news conference, she said: "With respect to the letter you referred to, I think that Mr Gaddafi knows what he must do.

"There need to be a ceasefire, his forces need to withdraw from the cities that they have forcibly taken..there need to be a decision made about his departure from power and...his departure from power."

Colonel Gaddafi sent the message "following the withdrawal of America from the crusader colonial alliance against Libya", Libya's official news agency JANA earlier said.