President Obama demanded Friday that Moammar Gadhafi halt all military attacks on civilians and said that if the Libyan leader did not stand down the United States would join other nations in launching military action against him.
But the president also stressed the United States "is not going to deploy ground troops into Libya."
In a brief appearance at the White House, Obama said Secretary of State Hillary Rodham Clinton would travel to Paris today to join allies in discussing the next steps in Libya, where Gadhafi has pressed a brutal crackdown against rebels trying to end his 42-year reign.
Stressing that the United States was acting in concert with European allies and Arab nations, the president said, "Our goal is focused, our cause is just and our coalition is strong."
Obama's remarks came less than 24 hours after the U.N. Security Council voted to authorize military action -- including a "no-fly zone" over Libya -- to prevent the killing of civilians by Gadhafi's forces.
Before his public announcement that U.S. forces would join in military action against Libya, Obama met at the White House with congressional leaders of both parties to discuss his thinking.
"The U.S. military will be playing a supportive role in this action. We will not have troops on the ground; instead we are providing strategic support where we have unique capabilities to the Arab and European nations that are taking the lead," said Rep. Howard Berman, D-Calif., the top Democrat on the Foreign Affairs Committee. He took part in the Obama session by telephone.
Speaking earlier, Sen. Lindsey Graham, R-S.C., said he believes Obama has authority to commit U.S. forces to participate in imposing a no-fly zone without congressional approval, but he expressed hope that Congress would bless the move.
At the White House, Obama said there should be no doubt about Gadhafi's intentions "because he has made them clear. Just yesterday, speaking of the city of Benghazi, a city of roughly 700,000, he threatened 'we will have no mercy and no pity.' No mercy on his own citizens."
The president has been criticized by some U.S. lawmakers and others for not moving more forcefully while Gadhafi has regrouped in recent days and taken the offensive against the rebels. Obama said the United States and other nations have imposed sanctions on Libya, frozen assets of the leader and delivered humanitarian supplies to bordering countries to help ease the plight of thousands fleeing the fighting.
"Now, once more, Moammar Gadhafi has a choice," Obama said, listing what he said were non-negotiable conditions laid out by the U.N. Security Council.
"If Gadhafi does not comply, the international community will impose consequences, and the resolution will be enforced through military action," Obama said.
He did not specify what responsibilities would fall to the United States if military action is carried out against Gadhafi, but officials have said previously that American forces would help enforce a no-fly zone to prevent the Libyan leader from using his air force to bomb civilians.
The president made no reference to Libya's declaration of an immediate cease-fire on Friday -- a statement that a rebel spokesman said was fiction.
Instead, Obama listed a series of demands for Gadhafi, including the halting of all attacks against civilians, a stop to military action against Benghazi and other cities and permission for humanitarian supplies to reach the civilian population of the country.
"Let me be clear, these terms are not negotiable," he said.
He emphasized that the United States was not acting alone but in concert with Britain, France and Arab countries he did not name.
Earlier, Clinton told reporters that Gadhafi must make "a very clear set of decisions" to halt violence against anti-government rebels.
Clinton said the U.S. had seen the reports of a cease-fire by the Libyan government, but she added that the American government was not going to be "impressed by words." She said the immediate objective of any intervention was to halt the violence against civilians, but insisted that the "final result of any negotiation would have to be the decision by Col. Gadhafi to leave."
The U.S. has ships and warplanes within striking distance of Libya, including submarines and surface ships armed with Tomahawk cruise missiles. If military action were to proceed, a first step likely would involve attacks on Libyan air defenses, including radar and surface-to-air missile sites along its Mediterranean coastline. That would allow aircraft enforcing a no-fly zone to maneuver with impunity.
Britain, France and NATO were holding emergency meetings Friday on using military force to enforce a no-fly zone. NATO Secretary-General Anders Fogh Rasmussen said the alliance was "completing its planning to be ready to take appropriate action in support of the U.N. resolution as part of the broad international effort."
The New York Times reported Friday that four journalists who were captured by Libyan forces during fighting in the eastern part of the country will be released.
The four planned to drive to the Egyptian border and fly out of Egypt, said Buddy Shadid, the father of Times reporter Anthony Shadid, one of the four. The others are photographers Tyler Hicks and Lynsey Addario and a reporter and videographer, Stephen Farrell.