President Barack Obama and British Prime Minister David Cameron discussed Tuesday how to bring about the departure of Libya's Muammar Gaddafi "as quickly as possible," Reuters reports.

Gaddafi's crackdown on the recent uprising in Libya has put the country on the verge of a humanitarian crisis.

The two leaders discussed "a full spectrum of possible responses" to Gaddafi's attacks on rebels, according to the White House. These options include surveillance of Libya with spy planes, humanitarian assistance and imposing a much-discussed no-fly zone over Libya to prevent pro-government forces from attacking civilians and protesters.

GlobalPost's David Case argues Obama must deploy the U.S. military to help Libya now.

"Obama needs to act not only because Gaddafi is intolerable, but because failing to intervene would be a victory for dictators across the globe," he writes. "These days, Gaddafi’s neighborhood is replete with besieged strongmen who are busy preparing for the Facebook revolution that’s targeting them. They are no doubt watching Libya closely to see how much murder they can get away with before risking Tomahawk missile attacks on their own palaces. By using the U.S. military to make Gaddafi writhe, the Obama administration can cauterize the worst of the protestor bloodshed before it is spilled."

As Libyan warplanes continued attacks on rebel-controlled cities, Britain and France said they were seeking U.N. authority for a no-fly zone over the country.

The European countries are drafting a U.N. resolution for a no-fly zone, and NATO will take up the issue on Thursday, the BBC reports. However, it said the issue was still dividing the international community.

"We are working closely with partners on a contingency basis on elements of a resolution on a no-fly zone, making clear the need for regional support, a clear trigger for such a resolution and an appropriate legal basis," British Foreign Secretary William Hague said Monday, according to Reuters.

U.S. President Barack Obama said the U.S. and its NATO allies were consulting on a “wide range” of potential responses, including military options, according to Bloomberg. Several Gulf states have expressed their support for the action.

NATO's squadron of sophisticated surveillance planes were reportedly circling off Libya's coast Tuesday, giving the alliance "a better picture of what is really going on,” according to Ivo Daalder, the U.S. ambassador to NATO, quoted in the Globe and Mail.

Meanwhile, up to 50 tanks and 120 pick-up trucks launched attacks Tuesday on the rebel-held town of Zawiya 30 miles from the Libyan capital, Tripoli.

"I don't know how many are dead — they tore Zawiya down to ashes," a source reportedly told the BBC.

Reports of massive damage from the all-out assault on the town, which rose up against the Gaddafi regime two weeks ago, were emerging, according to the Guardian.

The regime had cut all mobile and landline communications in Zawiya, and accounts of the fighting came from witnesses who had driven out of the combat area and one who had climbed on a roof to find a phone signal. They described women and children being killed by gunfire and mosques destroyed.

There were unconfirmed reports that Gaddafi had made contact with rebel leaders to propose a deal under which he would step down if he and his family were given guarantees and immunity from prosecution.

A leader of the Libyan rebel forces has vowed not to pursue Gaddafi for war crimes if he steps down within three days, according to reports. "If he leaves Libya immediately, during 72 hours, and stops the bombardment, we as Libyans will step back from pursuing him for crimes," Mustafa Abdel Jalil, an ex-justice minister, reportedly told Al-Jazeera Television.

In Washington, Obama stepped up pressure on Gaddafi's inner circle, urging them to step down and pave the way for reform, warning them they could face future prosecution for their roles in repressing the rebellion.

"I want to send a very clear message to those who are around Colonel Gaddafi," Obama said. "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."

Trying to persuade Gaddafi's inner circle to desert him has been a central part of the Obama administration's policy toward Libya, the Washington Post reports.

"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," it states.

Fighting between the rebels and forces loyal to Gaddafi continued to intensify with no sign of a break in the deadlock in struggles for key towns. There was heavy bombardment by government aircraft of the oil hub of Ras Lanuf Monday.

Families were fleeing the town to escape the violence by there were claims that helicopter gunships had opened fire on civilians, CNN reported.

The violence in Libya has left a million people in need of humanitarian assistance, according to the United Nations. "People are injured and dying and need help immediately," U.N. aid coordinator Valerie Amos said.

In Zawiya, 30 miles west of Tripoli, a correspondent from Sky News gave a graphic account of being trapped inside the rebel-held town as Gaddafi's troops mounted a sustained assault.

Snipers "killing civilians"

Writing in the Telegraph, she said an ambulance she was riding in had come under fire, described government snipers killing civilians and how she had seen one youth learning to use a rocket-launcher before rushing off to join the battle.

Meanwhile, a video purporting to show Libyan army officers being killed for refusing to fire on rebels was posted by Al Jazeera, which said the footage was potentially evidence of how Gaddafi deals with "traitors."

It quoted a survivor of the killings saying the men were tied up before being shot in the head or back at close range after they refused to attack rebels in mountains around Zawiya.

In Tripoli, Foreign Minister Musa Kusa offered the first government admission that Gaddafi's troops were meeting resistance in Zawiya, but played down claims of a full-scale battle, the New York Times reported.

Kusa also accused Britain and the United States of "yearning for the colonial era" and seeking to divide Libya. He also claimed a 300-strong force of former Guantanamo Bay inmates loyal to Al Qaeda was backing the rebels.

In Britain there was more fallout from a botched special forces mission to make diplomatic contact with the rebels. Foreign Secretary Hague took responsibility for the mission, which ended when elite SAS troops were captured by "farmers."

The Guardian newspaper said the "unilateral act of James Bond diplomacy" has potentially damaged British credibility and undermined Prime Minister David Cameron's efforts gain European Union backing for action against Gaddafi.

-- Hanna Ingber Win, Barry Neild, Freya Petersen