Syrian President Bashar al-Assad has pledged to destroy his stockpile of chemical arms but said it would take one year to do so and will cost about $1bn.

In an interview with Fox News, the US television channel, Assad also said his country was not gripped by civil war, but had been infiltrated by tens of thousands of foreign jihadists linked to al-Qaeda.

Assad's latest televised appearance came as UN envoys debated a draft resolution on Wednesday that would enshrine a joint US-Russian plan to secure and neutralise his banned weapons in international law.

The Syrian president denied on Wednesday that his forces were responsible for the chemical weapons attack outside Damascus on August 21, and attacked the UN report that found "clear and convincing evidence"' of the use of sarin nerve gas.

Assad said his army was advancing in the area at the time and had no need to fire rockets filled with the agent.

"The whole story doesn't even hold together. It's not realistic. So, no, we didn't. In one word, we didn't use any chemical weapons in Ghouta," Assad told Fox News.

Assad told the channel that chemical disarmament would be costly and complicated.

"It needs a lot of money, it needs about $1bn. It is very detrimental to the environment," he said.

"If the American administration is ready to pay this money and take the responsibility of bringing toxic materials to the United States, why don't they do it?"

He said his decision to destroy his stockpiles of chemical weapons was not forced upon him by the threat of a US strike, and that he was responding to the initiative by Russia and "our conviction".

"So whether they have Chapter VII or don't have Chapter VII, this is politics between the great countries," he said, referring to a UN rule that would have to be invoked to justify international action."

'Distorted and one-sided'

Earlier on Wednesday, Russia dismissed the UN report on the Damascus attack and said it had Syrian-supplied evidence that shows rebels were responsible.

Sergei Ryabkov, Russia's deputy foreign minister, said that Moscow was disappointed with the UN report, published on Monday, calling it "distorted and one-sided".

Ryabkov said said after talks with Assad in Damascus that the regime had given Russia material implicating rebel groups in the August 21 attack.

He told Russian television later that it was given to Ake Sellstrom, who headed the group of UN inspectors, but it did not "receive adequate attention in the report".

Sergey Lavrov, Russia's foreign minister, said Syria's evidence would be presented to the UN.

'Not conclusive'

The UN report did not ascribe blame but detailed munitions and rockets used in the Damascus attack, their likely point of origin and their capacity. One missile used could hold 56 litres of sarin gas. As little as 0.5mg of sarin can kill an adult.

The US holds Assad responsible for the attack, which it says killed 1,429 people. The regime denies responsibility and its ally Russia maintains that there is no evidence implicating Assad.

The UN later said its conclusions were beyond question. "The findings in that report are indisputable," UN spokesman Martin Nesirky said. "They speak for themselves and this was a thoroughly objective report on that specific incident."

Meanwhile, Human Rights Watch released its analysis of the UN report, saying that it showed two of the missiles fired on August 21 originated from a Republican Guard compound.

However, the evidence was "not conclusive".

Ryabkov is on a visit to Damascus to present the Syrian government with the results of the agreement between Russia and the US reached in Geneva, Switzerland, to rid Syria of its chemical weapons.

He said he emphasised to Walid al-Muallem, Syria's foreign minister, the importance of Damascus "strictly and swiftly" handing over details of its chemical weapons arsenal to the Organisation for the Prohibition of Chemical Weapons, the first step under the agreement.

Ryabkov said he assured the Syrian side that there was "no basis" for a UN Security Council resolution on the chemical weapons agreement to invoke Chapter VII of the UN Charter that allows the use of force and tough sanctions.

He said this could only be considered if the Security Council was able to confirm violations of the convention on chemical weapons. "This is a hypothetical situation," he said