President Obama addressed comments directly to Moammar Gaddafi’s inner circle Monday in an attempt to pressure those helping prop up the embattled Libyan dictator with a tacit threat of future criminal prosecution.

Much of the administration’s policy has been focused on persuading those around Gaddafi, who is confronting an armed rebel force seeking to end his 41-year rule, to actively turn against him.

In the days after the regime’s crackdown began, senior administration officials said, the United States appealed directly to Libyan Foreign Minister Musa Kusa, a former intelligence chief who has maintained ties with U.S. diplomats and CIA officials for more than a decade.

The Libyan minister spoke at length with U.S. officials by phone and was cautioned directly about the use of deadly force against protesters, according to two top administration officials familiar with the exchange who would describe it only on the condition of anonymity. But U.S. intelligence officials say Kusa has shown no sign of turning against Gaddafi and appears to have decided to remain with the government and his longtime commander.

The appeal to senior Libyan officials reflects the administration’s assessment that Gaddafi is unlikely to step down on his own, even under extreme pressure, and that the best way to dislodge him from power is to peel away his closest confidants.

The administration’s application of financial sanctions on senior Libyan officials, NATO’s increased satellite surveillance of military operations and the U.N. threat of an International Criminal Court indictment have been adopted to exert pressure on the inner circle. But Monday was the first time Obama addressed Gaddafi’s closest allies directly, warning: “We continue to monitor the violence there.”

“I want to send a very clear message to those who are around Colonel Gaddafi,” Obama said during an Oval Office appearance with visiting Australian Prime Minister Julia Gillard. “It is their choice to make, how they operate moving forward, and they will be held accountable for whatever violence continues to take place there.”

Obama spoke as forces loyal to Gaddafi fought to claw back territory lost to Libya’s armed opposition, including towns in and around the capital, Tripoli. Much of the country’s east is in rebel hands, and Gaddafi is deploying air and ground forces to retake many towns important to Libya’s oil industry — the lifeblood of the economy — and those providing a strategic cushion around Tripoli.

Debate over no-fly zone

The increasingly bloody stalemate on the ground is heightening calls for establishing a no-fly zone above Libya to protect rebel-held areas from government airstrikes. The idea is threatening to divide Washington along partisan lines, with Republican lawmakers arguing more strenuously for a no-fly zone than Democrats, although senators from both sides of the aisle have called for one.

Libya’s opposition forces have asked for a no-fly zone but have warned the United States and its European allies against sending any troops into the country.

Obama has been among the most cautious heads of state on the issue of military involvement in Libya, concerned that injecting the United States more directly into a third conflict in a Muslim nation would undermine the revolt’s popular nature.

The issue, along with less aggressive steps such as the electronic jamming of the Libyan government’s radio communications, will be taken up Thursday in Brussels at a meeting of NATO defense ministers.

NATO ambassadors agreed Monday to expand surveillance flights monitoring Libyan airspace, sea traffic and ground movement. Patrol flights of Airborne Warning and Control System, or AWACS, aircraft will increase from 10 to 24 hours a day.

The U.S. ambassador to NATO, Ivo Daalder, said countries were gathering information on the resources and logistics necessary to implement a no-fly zone. He said that “fighter and overall air activity” in Libya peaked last week and dropped over the weekend even as ground fighting intensified.

“It’s important to understand that no-fly zones are more effective against fighters, but they really have a limited effect against the helicopters or the kind of ground operations that we’ve seen, which is why a no-fly zone, even if it were to be established, isn’t really going to impact what is happening there today,” Daalder told reporters. “That doesn’t mean we shouldn’t look at it — and we are, and we will — but it is not going to be the solution to every problem.”

Administration officials have cautioned that preventing Libyan airstrikes would do little to thwart the harsh repression Gaddafi’s ground forces are carrying out in areas they control. But some human rights advocates have said that implementing a no-fly zone would send a message to Gaddafi’s inner circle that the international front against him was determined to oust the government.

“A no-fly zone might have a psychological impact on people around Gaddafi, impressing on them that they won’t be able to retake the rest of Libya and that their cause is a lost one, perhaps speeding the end of the standoff,” said Tom Malinowski, the Washington director of Human Rights Watch. “But, in the meantime, a no-fly zone would obviously provide no direct protection to the civilians being terrorized in Tripoli.”

Draft U.N. resolution

At the United Nations, Britain and France have taken the lead in drafting a Security Council resolution that would impose a no-fly zone and provide greater scope for humanitarian operations in Libya. But it would not authorize the use of military force to protect the delivery of humanitarian supplies inside Libya, according to officials.

No decision has been made to formally introduce the draft, according to council diplomats. They said any decision to move forward on it would require support from Libyans and regional organizations such as the Arab League and the African Union. It would also probably require evidence of large-scale killings of civilians.

Speaking Monday to the House of Commons, British Foreign Secretary William Hague said work on the resolution is being done “on a contingency basis” in case it is needed to stop the violence. He said it would “make clear the need for regional support, a clear trigger for such a resolution and an appropriate legal basis.”

The West is facing stiff resistance to the use of military force in Libya. Last week, the Arab League issued a statement voicing opposition to “foreign intervention” in Libya. Russian Foreign Minister Sergei Lavrov, whose country holds veto power on the council, said his government does not support outside military intervention. “The Libyans have to solve their problems by themselves,” he said.

Staff writers Colum Lynch at the United Nations and Mary Beth Sheridan in Washington contributed to this report.