Syrian artillery and warplanes pounded rebel areas in Damascus Saturday as President Bashar Al-Assad's foes pleaded for advanced weapons from the United States, which has promised them unspecified military aid.

Western powers have been reluctant in the past to arm Syrian insurgents, let alone give them sophisticated anti-aircraft missiles that might fall into the hands of Sunni Islamist insurgents in rebel ranks who have pledged loyalty to Al-Qaeda.

Free Syrian Army (FSA) commander Salim Idriss told Reuters Friday that rebels, who have suffered setbacks at the hands of Al-Assad's forces in recent weeks, urgently needed anti-aircraft and anti-tank missiles, as well as a protective no-fly zone.

"But our friends in the United States, they haven't told us yet that they are going to support us with weapons and ammunition," he said after meeting US and European officials in Turkey.

A source in the Middle East familiar with US dealings with the rebels has said planned arms supplies would include automatic weapons, light mortars and rocket-propelled grenades.

Russia, an ally of Damascus and fierce opponent of outside military intervention, warned Saturday against any attempt to enforce a no-fly zone over Syria using F-16 fighter jets and Patriot air defence missile systems from Jordan.

"You don't have to be a great expert to understand that this will violate international law," Foreign Minister Sergei Lavrov told a news conference with his Italian counterpart in Moscow.

Western diplomats said Friday that the United States was considering a no-fly zone over Syria, but the White House said later that it would be far harder and costlier to set up one in Syria than it was in Libya, stressing that the United States has no national interest in pursuing that option.

Outgunned rebels have few ways to counter Al-Assad's air power. The pro-opposition Syrian Observatory for Human Rights said Saturday jets and artillery had attacked Jobar, a battered district where rebels operate on the edge of central Damascus.

It said heavy artillery was also shelling opposition fighters in the provinces of Homs, Aleppo and Deir Al-Zor.

A Turkish official said 71 Syrian army officers, including six generals, had defected to Turkey, in the biggest single mass desertion from Al-Assad's military in months.

The United Nations says at least 93,000 people, including civilians and combatants, have died in the Syrian civil war, with the monthly death toll averaging 5,000 in the past year.

Military balance

On Thursday, a US official said President Barack Obama had authorised sending US weapons to Syrian rebels for the first time, after the White House said it had proof the Syrian military had used chemical weapons against opposition forces.

Abu Nidal, from the Islamist Ahrar Al-Sham rebel group, said US help was welcome, but questioned how effective it would be.

"I doubt the influx of weapons will significantly tip the balance into our favour," he said via Skype. "They might help push back regime offensives of the last few days."

Abu Nidal's faction is not part of the more moderate FSA, Washington's chosen channel for military aid, but he said the two groups fight alongside each other on the battlefield.

"We are not at odds with the Free Syrian Army now. We fight in one formation," the Islamist fighter said.

Other opposition sources have also voiced scepticism over what type and quantity of arms the United States would deliver.

The surface-to-air missiles that rebels say they need to ward off Al-Assad's air force are particularly worrisome for Western powers as they could be used against commercial jets.

Since the anti-Assad revolt erupted in March 2011, Western nations have demanded the Syrian leader's ouster, but have not used force as they did to back Libyans fighting Muammar Gaddafi.

Intervening against Al-Assad is considered riskier because Syria has a stronger military, sits on the sectarian faultlines of the Middle East, and is supported by Iran and Russia, which has vetoed three UN Security Council resolutions on Syria.

Yet an apparent shift in the military momentum in Al-Assad's favour, especially with the arrival of thousands of fighters from Lebanon's Iranian-backed Hizbullah group, has made his swift removal look unlikely without outside intervention.

However, Israel's defence minister suggested the pendulum could still swing the other way, despite the capture this month of Qusair, a former rebel stronghold near the Lebanese border.

"Bashar Al-Assad's victory in Qusair was not a turning point in the Syrian civil war, and I do not believe that he has the momentum to win," said Moshe Yaalon, who is visiting Washington.

"He controls just 40 percent of the territory in Syria. Hizbullah is involved in the fighting in Syria and has suffered many casualties in the battles, and as far as we know, it is more than 1,000 casualties," Yaalon said in a statement.

"We should be prepared for a long civil war with ups and downs."

It was not immediately clear why the group had deserted. Just hours ago, the United States said it would arm Syrian rebels, having obtained what it says is proof that Al-Assad's forces used chemical weapons against fighters trying to end Al-Assad's rule.