DAMASCUS: Syria's main opposition group on Tuesday demanded a swift international response following the report by the United Nations (UN) confirming the use of chemical weapons in Syria.

Damascus, in turn, slammed the United States (US), British and French foreign ministers, accusing them of trying to impose their agenda on the Syrian people.

The Foreign Ministry statement appeared to be in response to demands by the foreign ministers of France, Britain and the US that Syrian President Bashar Assad, step down even as the West increases efforts to bring the warring sides to an international peace conference.

''Assad is the legitimate president chosen by the Syrian people and will remain so as long as the Syrian people want this,'' said the Syrian Foreign Ministry.

The statement comes after the UN report was released Monday, which was the first official confirmation by impartial experts that chemical weapons were used in the August 21 attack near Damascus that killed hundreds of people.

The Western-backed Syrian National Coalition said the UN report offered ''damning and irrefutable evidence'', and clearly shows that only the Syrian regime could have carried out the attack last month. UN chief Ban Ki-moon told the Security Council when he presented the report earlier that the attack was a ''war crime.''

''The results are overwhelming and indisputable. The facts speak for themselves,'' Ban said.

The report, he said, was ''the most significant confirmed use of chemical weapons against civilians since Saddam Hussein used them'' in Halabja, Iran, in 1988, and ''the worst use of weapons of mass destruction in the 21st century.''

The Syrian opposition said there must be a swift response and called on the UN to refer Syria to the International Criminal Court.

''The Syrian coalition urges the Security Council to end the culture of impunity in Syria, and to stop the Syrian regime from carrying out further war crimes and crimes against humanity,'' the Coalition demanded.

The UN inspectors report was careful not to blame either side in the Syrian civil war for the attack.

While it stated surface-to-surface rockets loaded with the nerve agent sarin had been fired from an area where Syria's military has bases, it also said the evidence could have been manipulated in the rebel-controlled neighborhood that was struck.

The US, Britain and France jumped on evidence in the report - especially the type of rockets, the composition of the sarin agent, and trajectory of the missiles - to declare that Assad's government was responsible. Russia, a staunch ally of the Syrian regime, disagreed.

Damascus on Tuesday blasted the foreign ministers of the US, France and Britain for ''their frantic quest to impose their will'' on the Syrian people.

The Foreign Ministry said any talk about the political and constitutional legitimacy in Syria is an ''exclusive right for the Syrian people and it is impermissible for the United States, its allies and tools'' to impose their will in this regard.

''The allegations by the US and its allies about commitment to achieve a political solution for the crisis in Syria to end violence contradict their continuing attempts to precede the political process and impose prior conditions on it,'' the ministry said.

Earlier on Tuesday, the Syrian military accused Turkey of seeking to escalate tensions along the two nations' already volatile border by shooting down a Syrian military helicopter the the day before.

The military said the helicopter was on a mission to monitor for cross-border infiltration of rebels when it ''mistakenly'' entered Turkish airspace.

Turkey's deputy prime minister Bulent Arinc told reporters in Ankara on Monday that the aircraft was shot down by a fighter jet after it ignored repeated warnings to leave Turkish airspace.

The helicopter had strayed two kilometers over Turkey but crashed inside Syria after being hit by missiles fired from the Turkish jet. Arinc said he did not have any information on the fate of the Syrian pilots.

The Britain-based Syrian Observatory for Human Rights said rebel fighters captured one of the two crew members, while the fate of the other was unclear. The Syrian military said the helicopter entered Turkish space ''for a short distance'' by mistake.

''The hasty reaction from the Turkish side, particularly that the helicopter was heading back and was not on a fighting mission, reveals the real intentions'' of Ankara to ramp up tensions, it said.

Turkey has been at odds with the Syrian government since early in the country's civil war and has backed the Syrian rebels, while advocating international intervention in the conflict.

Turkish Foreign Minister Ahmet Davutoglu, speaking in Paris after meetings about Syria with his counterparts from other countries, said Monday's incident should send a message.

''Nobody will dare to violate Turkey's borders in any way again,'' he said, according to Anatolia, the Turkish state-run news agency. ''The necessary measures have been taken.''