"Our duty and our mandate under U.N. Security Council Resolution 1973 is to protect civilians, and we are doing that. It is not to remove Gaddafi by force," they write.

"But it is impossible to imagine a future for Libya with Gaddafi in power. The International Criminal Court is rightly investigating the crimes committed against civilians and the grievous violations of international law. It is unthinkable that someone who has tried to massacre his own people can play a part in their future government," the trio write.

"Even as we continue our military operations today to protect civilians in Libya, we are determined to look to the future," they write. "We are convinced that better times lie ahead for the people of Libya, and a pathway can be forged to achieve just that. "

They call for a genuine end to violence, "marked by deeds not words" in which the government forces have to pull back from the cities they are besieging and return to their barracks.

Britain and France, which are spearheading the airstrikes on Libya after NATO took over control of the mission from the United States on March 31, have grown frustrated with the lack of support from allies as stalemate continues on the ground in Libya. But the United States has been resisting calls for its reasserting a stronger role in the airstrikes.