Libyan leader Moammar Gadhafi's four-decade-long rule over Libya was crumbling at breakneck speed Sunday as hundreds of rebel fighters swept toward the heart of Tripoli and dissidents said they had secured control of many parts of the capital.
With rebel leaders saying that Gadhafi's compound was surrounded, that his son Seif al-Islam had been captured and that his presidential guard had surrendered, the 6-month-old battle for control of Libya appeared to be hurtling toward a dramatic finale.
By early this morning, rebels were firmly in control of the symbolically significant Green Square in the heart of the city. In a brief broadcast on state television, Gadhafi made what came across as a desperate plea for support. "Go out and take your weapons," the Libyan leader said.
President Obama said Sunday night that the situation in Libya has reached a "tipping point" and that control of the capital was "slipping from the grasp of a tyrant." He called on Gadhafi to accept reality and relinquish power.
"The surest way for the bloodshed to end is simple: Moammar Gadhafi and his regime need to recognize that their rule has come to an end," Obama said in a statement issued while on vacation in Martha's Vineyard, Mass. "Gadhafi needs to acknowledge the reality that he no longer controls Libya. He needs to relinquish power once and for all."
Obama issued the statement after conducting a conference call with members of his national security team, who had provided him with updates throughout the day.
The rebel advance unfolded with surprising speed throughout the day as fighters converged on the capital from three directions.
In areas under rebel control, thousands of people poured onto the streets to celebrate, stomping on posters of Gadhafi, setting off fireworks and honking horns. Opposition flags fluttered over buildings around Tripoli, including those around the central square, previously the site of near-daily pro-Gadhafi rallies.
"Now we don't call it the Green Square, but we call it the Martyrs Square," said Nour Eddin Shatouni, a 50-year-old engineer who was among the residents who flowed out of their homes to join the celebrations. "We were waiting for the signal and it happened. All mosques chanted 'God is great' all at once. We smelled a good scent, it is the smell of victory. We know it is the time."
With communications to the capital sporadic and some journalists confined to their hotel, some rebel claims could not be confirmed, and some experts cautioned that a tough urban battle may yet lie ahead between the lightly armed and untrained rebels and the elite government forces kept in reserve for the defense of the capital.
But reporters traveling with rebel forces said Gadhafi's defenses were melting away faster than had been expected, with reports of entire units fleeing as rebels entered the capital from the south, east and west, and his supporters inside the city tearing off their uniforms, throwing down their weapons and attempting to blend into the population.
A Tripoli-based activist said the rebels had secured the seaport, where several hundred reinforcements for the opposition had arrived by boat, and were in the process of evicting Gadhafi loyalists from the Mitiga air base on the eastern edge of the city.
NATO Secretary-General Anders Fogh Rasmussen said Gadhafi's regime was "clearly crumbling" and that the time to create a new democratic Libya has arrived.
NATO's 5-month-old aerial bombing campaign, ostensibly launched to protect civilians, contributed enormously to the erosion of government defenses.
The sooner Gadhafi "realizes that he cannot win the battle against his own people, the better," Rasmussen said in a statement, adding that NATO will continue to strike his troops if they make "any threatening moves toward the Libyan people."
A U.S. official in Washington who was monitoring the intelligence from Libya said that the situation in Tripoli was fluid but that it was unlikely Gadhafi and his hard-core loyalists would give up easily.
In the rebel capital, Benghazi, where huge crowds gathered to celebrate what they hoped was the imminent capture of Tripoli, Transitional National Council leader Mustafa Abdel Jalil announced that Gadhafi's son had been captured.
The prosecutor at the International Criminal Court in the Netherlands said he would contact the rebels to discuss al-Islam's handover for trial.
Gadhafi, al-Islam and Libya's intelligence chief were indicted earlier this year for allegedly ordering, planning and participating in illegal attacks on civilians in the early days of the violent crackdown on anti-regime protesters.
There was no indication as to Gadhafi's whereabouts, though he had issued a defiant speech earlier in the day in which he insisted he was in Tripoli and would not surrender.
"We cannot go back until the last drop of our blood. We will defend the city. I am here with you," he said in the audio statement, purportedly broadcast live. "Go on, go forward!"
But it appeared that his control had already unraveled as the rebels swept into the capital, encountering only pockets of resistance along the way.
State Department spokeswoman Victoria Nuland said officials there are turning their attention to post-Gadhafi Libya. "Gadhafi's days are clearly numbered," she said. "If Gadhafi cared about the Libyan people, he would step down now."
The Associated Press contributed to this report.