Troops loyal to longtime Libyan leader Muammar Gaddafi have capitalised on an apparent slowdown in the frequency of coalition air strikes in the east and have pushed back opposition rebels, taking the strategic oil town of Ras Lanuf.

Regime forces shelled rebel fighters with mortars and possibly Grad rockets on Wednesday, forcing them to retreat from Bin Jawad through Ras Lanuf, more than 200 kilometres east of Sirte, Gaddafi's well-defended hometown.

The reversal for Libya's nascent opposition came after their forces had made a speedy, two-day advance from Ajdabiya under the protection of international air cover.

Libya map - all cities

The rebels had advanced 20 kilometres beyond Bin Jawad on Monday, reaching the village of Nawfaliya before meeting stiff resistance. After shelling on Tuesday, they fell back to Ras Lanuf, a major coastal oil facility, and then appeared to lose the town entirely on Wednesday.

The sound of jet aircraft could be heard in the skies above the fighting, as well as explosions that seemed to indicate air strikes were taking place on the road between Ras Lanuf and Brega, the next strategic town on the road to Ajdabiya. But the possible air strikes didn't seem to help the rebels hold their defenses.

Rebels rely on air cover

For 10 days, an international coalition including forces from France, the United Kingdom, the United States and Qatar has been patrolling the skies and pounding Gaddafi's troops and facilities on the ground in order to enforce a UN Security Council resolution aimed at protecting Libyan civilians.

The military campaign opened a path for the rebels to advance out of Benghazi, the opposition's eastern stronghold, which Gaddafi's troops had threatened to overrun on March 19.

If the regime troops continue to advance east down the main coastal road toward Ajdabiya, an important crossroads and the last major town before Benghazi, they could expose themselves to coalition jets, who could "pick off tanks" as they have done before, Al Jazeera's Sue Turton, in Benghazi, said.

But on Wednesday, control of the no-fly and "no-drive" zone is set to pass into NATO hands after days of slow negotiations during which Turkey - a NATO member - reportedly raised objections to the aggressive coalition ground attacks.

It remains to be seen whether the switch in command will involve a shift in tactics away from the intensive ground attacks that drove Gaddafi's tank columns back from Benghazi and, the rebels say, saved the city from a massacre.

Opposition fighters in the western town of Misurata have also come under renewed attack from pro-Gaddafi forces, an opposition spokesman there said on Tuesday.

He said eight civilians had died that day and described the humanitarian situation in Misurata as "catastrophic," with water and electricity cut off and residents running short of essential supplies, including medicines.

Arming the rebels

The stall in the rebel advance has raised questions about the need to supply the opposition with weapons. For the past two days, untrained rebels have been powerless to stand against the bombardment from regime troops.

"They have nothing like the weight of firepower that Gaddafi's forces have," Turton said.

During a 40-nation conference on Libya held in London on Tuesday, US Secretary of State Hillary Clinton left the door open to arming the rebels.

"It is our interpretation that [Security Council] resolution 1973 amended or overrode the absolute prohibition [on providing] arms to anyone in Libya," Clinton said. "So there could be a legitimate transfer of arms, if a country were to choose to do that."

In an interview with NBC News Barack Obama, the US president, also refused to rule out the possibility.

"I'm not ruling it out," Obama said. "But I'm also not ruling it in. We're still making an assessment partly about what Gaddafi's forces are going to be doing."

Arming the rebels raises several controversial issues for the United States. It might necessitate sending in American troops to help train the fighters, and it would mean handing over weapons to forces whose composition is not entirely known.

Both issues have raised concerns among US legislators and are not likely to disappear, especially after NATO's top commander, US Admiral James Stavridis, testified before the US Senate on Tuesday that he had seen "flickers" of intelligence indicating Hezbollah and al-Qaeda involvement among the rebels.

Turton said opposition officials in Benghazi, most of them "everyday people", aren't concerned about an extremist influence in their ranks.

"It is a conservative society here in Libya, but they're not talking about those people within their ranks, and their concern is that that's the sort of proaganda, they say, that Colonel Gaddafi was putting out when they first started this push against him, and in a way, even talking about it is playing into his hands," she said.

Obama justifies intervention

Hours before the rebel retreat from Bin Jawad, Barack Obama, the US president, defended his country's involvement in the military campaign in Libya in a televised address to the nation.

Speaking to military officers and reporters at the National Defence University in Washington on Monday night, Obama said he refused to wait for images of the slaughter of civilians before taking action.

Obama said the Western-led air campaign had stopped Gaddafi's advances and halted a slaughter that could have shaken the stability of an entire region and "stained the conscience of the entire world".

"Some nations may be able to turn a blind eye to atrocities in other countries," he said. "The United States of America is different."

But he said that broadening the international mission to include regime change would be a mistake.

"If we tried to overthrow Gaddafi by force, our coalition would splinter," he said.

The US took the initial lead in the Western-led military action against Gaddafi before the recent NATO decision to take over the operations. Obama said the United States will transfer control to NATO on Wednesday.

Obama said once that transfer occurs, the risk and cost to US taxpayers will be reduced significantly.

Al Jazeera's Patty Culhane, reporting from Washington, said Obama's speech had two striking contradictions.

"The president said we must stand alongside those who work for freedom and at the same time he said we cannot be the policeman of the world only when it applies to our national interest," Culhane said.

"The president [seems to] be trying to explain why we have seen a lesser response to allies like Bahrain or Yemen."

Obama did not discuss plans for disengagement.

Source: Al Jazeera and agencies