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, yet reports from witnesses in Libya make it clear the fighting has not stopped.

Though Libya had agreed to a ceasefire earlier in the day, the "reports from rebel-held territory indicated that the attacks by Qaddafi militias continued unabated in the east and west."

The New York Times reports, "Government forces continued to advance on Benghazi, the rebel’s capital in the east, and people fleeing nearby Ajdabiya said troops were bombing and conducting assaults in the afternoon. The western city of Misurata was under siege, its electricity and water cut by the government, and doctors reported that at least 25 people were killed, including 16 unarmed civilians. In Tripoli, the repression of peaceful protests continued, and gunfire was heard late in the evening...[E]xplosions could be heard about 30 miles away from Ajdabiya. Residents who left the city after the cease-fire declaration said the announcement of an end to hostilities had in fact caused no break in the fighting."

Obama said Gaddafi must "accept an immediate ceasefire, pull back from Libyan rebel strongholds and permit humanitarian assistance," in what the president 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."

For his part, Gaddafi has denied any violence against his people and referred to the U.N. resolution as "blatant colonialism."

"It does not have any justification," he said. "This will have serious consequences on the Mediterranean and on Europe. There must be safe air or sea navigation whatever the case. In 2011 they are colonising us, massacring us, and imposing one no-fly zone after the other and one military attack after an other. What is this racism? What is this hatred?

Libya's Deputy Foreign Minister Khaled Kaim told Reuters there has been "no bombardment of any kind" by government forces since the ceasefire was announced.

Though reports said Gaddafi forces were heading toward Benghazi, Kaim said, "We have no intention of entering the city of Benghazi.”