Damascus and key ally Moscow joined forces on Wednesday in a bid to thwart plans for a Western-backed UN resolution on Syria's chemical weapons that allows the use of force.

The United States, meanwhile, said it will maintain the threat of force in case Syria's regime fails to abide by an agreement to relinquish control of its chemical weapons.

Russia came out swinging, saying Damascus had handed over new evidence implicating the rebels in an August 21 sarin gas attack near the capital that killed hundreds, while slamming a UN report into the incident as "biased."

Syrian President Bashar al-Assad, boosted by a visit to Damascus by Russian Deputy Foreign Minister Sergei Ryabkov, thanked Moscow for its support throughout his regime's 30-month-old conflict with armed rebels.

"President Assad expressed... his gratitude to Russia for its position of helping Syria face down the savage attack... and the Western, regional and Arab-backed terrorism," state television quoted him as saying after meeting Ryabkov.

"Russia's positions on the Syrian crisis create hope of a new global balance," Assad added.

His comments came as UN chemical weapons inspectors confirmed they would be returning to Syria for additional investigations into the use of the deadly weapons in the conflict.

Russia and the United States continued to trade accusations about who was to blame for the sarin attack that the chemical weapons inspectors confirmed in a report this week.

Despite having jointly agreed a deal under which Syria will turn over its chemical weapons stock, the two nations remain at loggerheads over who launched the attack.

The US military will maintain the threat of force against Syria, US Defence Secretary Chuck Hagel said Wednesday.

"We should keep that military option exactly where it is. We have assured the president that our assets and force posture remain the same," he told a news conference.

Russia said the Syrian regime had handed over new evidence implicating the rebels in the deadly incident and that this would be handed over to the United Nations.

Moscow will review the new materials and "of course, present them in the UN Security Council," Russian news agencies quoted Foreign Minister Sergei Lavrov as saying.

But US President Barack Obama has said it was "inconceivable" that anyone other than the Syrian regime could have carried out the attack.

Chapter VII resolution

The international community is also divided over the wording of a UN Security Council resolution on the US-Russia deal, with Moscow strongly opposing a Chapter VII resolution.

Syria's deputy foreign minister, Faisal Muqdad, told AFP on Wednesday that Damascus was confident the UN would not adopt a Chapter VII resolution.

"I think this is a big lie used by the Western powers; we believe it will never be used," he said in Damascus.

France and Britain are reportedly preparing a draft resolution including a demand for action under Chapter VII -- which allows the use of force and tough sanctions -- if Syria fails to uphold the deal on its chemical weapons.

But Russia has said there was "no basis" for a UN resolution to invoke Chapter VII.

Nick Brown, editor of the specialised IHS Jane's Defence Equipment and Technology Centre, said the UN report did not conclusively point any finger of blame.

"I have not personally seen any compelling data that proves beyond doubt who the weapons were used by," he said in an analysis to clients.

"The exact forensic detail of who prepared and then triggered the weapons remains unclear...

"The extremely fluid nature of the conflict in Syria makes it extraordinarily difficult to comment on the origin of weapons use in absolute terms," Brown wrote.

Ryabkov said on Tuesday that Syria had handed over new evidence showing opposition forces were behind the sarin attack.

He also said Russia was disappointed with the UN inspectors' report on the attack, describing it as selective for having ignored other alleged attacks.

"Without a full picture... we cannot describe the character of the conclusions as anything other than politicised, biased and one-sided," Russian news agency RIA Novosti quoted him as saying.

France rejected the claims of bias, saying "nobody can question of the objectivity of the people appointed by the UN."

UN chief inspector Ake Sellstrom, meanwhile, told AFP that his team would return to Syria to investigate additional alleged attacks.

The deal under which Syria will turn over its chemical weapons came after Washington threatened military action against Damascus in response to last month's chemical attack.

The agreement has halted talk of military action for now, but NATO Secretary General Anders Fogh Rasmussen said on Wednesday that the threat of military action should remain to ensure Syria keeps its promises to give up chemical weapons.

In the latest fighting, at least four regime air raids hit Barzeh in northern Damascus, said the Syrian Observatory for Human Rights.

And it said Kurdish fighters had forced jihadists to withdraw from a village in the northeast after clashes killed 21 on both sides.

The conflict that broke out in March 2011 has killed more than 110,000 people, according to rights groups, and several million refugees have flooded countries in the region and beyond.

...,/.,