Syrian President Bashar al-Assad claims an alleged poison gas attack blamed on his government last week was "100 percent fabrication" used to justify a US air strike.
“Syria's military had given up all its chemical weapons in 2013 after an agreement made at the time, and would not have used them anyway,” Mr Assad told AFP.
The US and its allies say the Syrian military carried out the attack, something Syria has already denied.
The April 4 attack in the town of Khan Sheikhoun killed scores of people and prompted the US to launch a cruise missile strike on a Syrian air base in response, its first direct assault on the Assad government in the six-year-old conflict.
Mr Assad said Syria would only allow an "impartial" investigation into the poison gas incident. On Wednesday Syria’s ally Russia vetoed a UN Security Council resolution to condemn the attack and push the Syrian government to cooperate with investigators.
Russia said the gas was part of rebel stockpiles, which the rebels have denied.
It was the deadliest such incident since a sarin gas attack killed hundreds of people in a rebel-held suburb of Damascus in 2013, prompting threats of US military action.
Samples taken from Khan Sheikhoun last week tested positive for the nerve agent sarin, the UK delegation at the global chemical weapons watchdog said on Thursday.
Turkish President Tayyip Erdogan and Russian President Vladimir Putin have agreed to support an investigation by the Organisation for the Prohibition of Chemical Weapons (OPCW) into the chemical weapons attack in Syria last week, Turkish presidential sources say.
In a Thursday phone call, Erdogan stressed to his Russian counterpart that the use of chemical weapons was a crime against humanity, they said.
The April 4 attack in the town of Khan Sheikhoun, blamed by many governments on the forces of Syrian President Bashar al-Assad, killed scores of people and prompted the US to launch a missile strike on a Syrian air base in response.