By Caren Bohan and Steve Holland
WASHINGTON (Reuters) - President Barack Obama said on Friday the United States and its allies are slowly "tightening the noose" on Libyan leader Muammar Gaddafi and that a no-fly zone remains an option to put pressure on him.
Obama, accused by critics of reacting too slowly to the turmoil in Libya, said he believes international sanctions, an arms embargo and other measures are having an impact and that all other options remain on the table.
"Across the board we are slowly tightening the noose on Gaddafi. He is more and more isolated internationally," Obama said. "I have not taken any options off the table."
Obama said the world had a duty to prevent a repeat of the atrocities in the Balkans during the 1990s. Developments on the ground in Libya must be watched closely and decisions about potential actions made on a case-by-case basis, he said.
Critics are pushing for more forceful intervention, including direct military aid to outgunned rebel groups made up of enthusiastic but ill-trained civilians and rogue soldiers.
The latest appeal for action came from former President Bill Clinton, who said the United States should enforce a "no-fly zone" over Libya to allow a fair fight between insurgents and troops loyal to Gaddafi.
"I wouldn't do it if they hadn't asked, but if the (insurgent) leaders are on television pleading for it, I think that we should do it," Clinton told a conference in New York late on Thursday.
U.S. Secretary of State Hillary Clinton, the former president's wife, has emphasized the need for U.N. approval for any intervention in Libya.
Obama said a no-fly zone will be discussed by NATO next Tuesday but any U.S. military involvement must be carefully considered.
"Any time I send the United States forces into a potentially hostile situation, there are risks involved and there are consequences and it is my job as president to make sure that we have considered all those risks," Obama said.
Secretary of State Clinton is due to meet next week with representatives of the Libyan opposition. Obama said a U.S. official will be assigned to interact with the Libyan opposition and determine ways the United States can assist it.
Obama sidestepped a question on whether it would be acceptable for the United States for Gaddafi to stay in power, repeating his position that the long-time Libyan leader should give up power.
(Editing by John O'Callaghan and John Whitesides)