With Libyan leader Muammar al-Qaddafi under growing pressure, the U.S. intelligence community now sees signs that his inner circle may be cracking.
Morale among Qaddafi's forces is extremely low, and his all-important inner circle -- a dozen people or less -- are now questioning whether the Libyan leader can survive, a senior U.S. official told Fox News.
Qaddafi's "inner circle" includes a handful of senior military officers, his immediate family and a handful of his political cronies, the senior official told Fox News.
Though rebel forces probably don't have the ability to out-gun Qaddafi's forces, U.S. officials say it may be the political dynamics -- not conditions on the ground -- that force Qaddafi's hand.
Qaddafi is said to be extremely isolated and constantly on the move -- likely rarely staying in one location for long.
On the ground in Libya, rebel forces continued a push westward Monday through oil towns toward the capital of Tripoli. But the opposition forces remain woefully outgunned by Qaddafi's forces, who swept the insurgents from positions in eastern Libya until the international intervention forced government troops to withdraw.
Rebels acknowledged they could not have held their ground without international airstrikes, as Obama delivered remarks to the American people Monday night defending his decision to send U.S. forces to the war-torn country, while refusing to send in ground troops.
Obama stressed that he would not commit the U.S. military to toppling Qaddafi's regime, warning that such a goal of regime change would fracture the coalition and require ground forces. He described that mission, rather, as one for the Libyan people, claiming the United States and its allies have "stopped Qaddafi's deadly advance" and will "keep the pressure" on his regime as the rebels continue fighting.
Obama's address comes after rebel fighters moved Monday about 70 miles west from the coastal oil terminal and town of Ras Lanouf to just beyond the small town of Bin Jawwad, where their push was halted by government fire along the exposed desert highway and the heavily mined entrance to Sirte.
The rebels are currently just 60 miles from Sirte, the bastion of Qaddafi's power in the center of the country.
Take control of that, and there's only the largely rebel-held city of Misrata — and then empty desert — in the way of the capital. Sirte could therefore see some of the fiercest fighting of the rebellion, which began on Feb. 15.
"Qaddafi is not going to give up Sirte easily because straightaway after Sirte is Misrata, and after that it's straight to Qaddafi's house," said Gamal Mughrabi, a 46-year-old rebel fighter. "So Sirte is the last line of defense."
He said there are both anti- and pro-Qaddafi forces inside Sirte.
Some residents were fleeing Sirte, as soldiers from a brigade commanded by Qaddafi's son al-Saadi and allied militiamen streamed to positions on the city's outskirts to defend it, witnesses said. Sirte was hit by airstrikes Sunday night and Monday morning, witnesses said, but they did not know what was targeted.
The city is dominated by members of the Libyan leader's Gadhadhfa tribe. But many in another large Sirte tribe — the Firjan — are believed to resent his rule, and rebels are hoping to encourage them and other tribes there to help them.
"There's Qaddafi and then there's circles around him of supporters. Each circle is slowly peeling off and disappearing," said Gen. Hamdi Hassi, a rebel commander speaking at the small town of Bin Jawwad, just 18 miles from the front.
The Associated Press contributed to this report.
Catherine Herridge is an award-winning Chief Intelligence correspondent for FOX News Channel (FNC) based in Washington, D.C. She covers intelligence, the Justice Department and the Department of Homeland Security. Herridge joined FNC in 1996 as a London-based correspondent.