President Obama issued a stern warning to Libyan leader Moammar Gaddafi Friday that if he failed to stop attacking civilians, the United Nations would enforce a no-fly zone.

Gaddafi must "accept an immediate ceasefire, pull back from Libyan rebel strongholds and permit humanitarian assistance," in what Obama called a "non-negotiable ultimatum."

The Guardian reports:

"In an attempt to reassure Middle East opinion and his own domestic audience, Obama said the US would help to co-ordinate a no-fly-zone, but not lead an operation that will include French, British and Arab jets.

The US president issued his warning after Gaddafi's foreign minister, Moussa Koussa, claimed he would accept a ceasefire in the wake of the UN security council resolution passed late on Thursday night authorising "all necessary measures short of an occupation force" to protect civilians.

In a stark message, Obama said: 'Muammar Gaddafi has a choice. The resolution that was passed lays out very clear conditions that must be met. The United States, the United Kingdom, France and Arab states agree that a ceasefire must be implemented immediately.'"

Obama spoke of the peril the country currently faces and the larger effects of Gaddafi's actions. 

“Just yesterday, speaking of the city of Benghazi, a city of roughly 700,000 people, he threatened, and I quote, ‘We will have no mercy and no pity.’  No mercy on his own citizens.”

He continued, "Left unchecked, we have every reason to believe that Gadhafi would commit atrocities against his people.  Many thousands could die. A humanitarian crisis would ensue. The entire region could be destabilized, endangering many of our allies and partners. The calls of the Libyan people for help would go unanswered."

In a statement, Senate Majority Leader Harry Reid of Nevada, said, “I believe the broad multilateral approach the President laid out will greatly improve the effectiveness of our efforts. The coalition we are working with includes not just our European allies, but also members of the Arab League. Qaddafi has lost legitimacy and it is only a matter of time before he is out of power. Together with our allies, we should work to ensure that Qaddafi’s transition out of power is swift, and that the people of Libya do not suffer any more than they already have.”