Syria's Foreign Minister Walid al-Moallem said on Thursday that the Syrian airstrike on the Islamic State-held town of Khan Sheikhoun struck a rebel depot containing chemical materials, and denied that the air force dropped poisonous gas bombs.

At a press conference held to comment on the international accusation that Syria allegedly fired toxic gas on Khan Sheikhoun in Idlib province on Tuesday, al-Moallem said the news reports were "lies".

He said it is not logical to use chemical weapons at a time when the Syrian government was optimistic that the international community was becoming closer to realising the extent of conspiracy against Syria.

He also asked how could the world powers be so quick to hurl accusation against the Syrian government within an hour of the attack.

The minister repeated his government's denial that "The Syrian army forces have not and will not use chemical weapons", and that the forces were no longer in possession of such weapons.

Al-Moallem said Al Qaeda-linked Nusra Front and like-minded groups have been storing chemical materials they brought into Syria from Iraq.

The minister also said there were probably several reasons behind the accusation.

The first was to reverse the opinion of US President Donald Trump, who said after the attack that his opinion toward the Syrian government has changed. Previously, the US administration said that toppling President Bashar al-Assad was no longer a priority.

The second reason, al-Moallem said, was to exert pressure on Russia not to aid the Syrian army, which Moscow had said it will continue to in the fight against terrorist groups.

The third reason is to exert pressure on Damascus, which he said will not change its approach to fighting terrorism and will work on political solution at the same time.

The minister said a change in the stance that Trump talked of could have been achieved by the attack.

"I realise the seriousness of the American remarks and maybe their aim is to practice pressure on the Russian and Chinese sides toward the UN draft resolution" put forward on Wednesday, he said.

The draft resolution, proposed by the US, France and Britain, called on Syria to provide flight plans, flight logs and other information on its military operations on the day of the assault.

Damascus would be asked to provide the names of all commanders of helicopter squadrons to UN investigators and allow them to meet with generals and other high-ranking officials within five days of their request, the draft resolution said.

According to the draft, Syria would also allow UN and Organisation for the Prohibition of Chemical Weapons (OPCW) teams to visit air bases from which the attacks involving chemical weapons may have been launched.

The draft threatened to impose sanctions under the UN Charter. Russia rejected the draft resolution.

About the possibility of forming an international probing mission to investigate the attack, the Syrian Minister said the mission should be organised and not politicised and "then there will be nothing wrong with that".

He added that his government was fully coordinating with the Russian side.

In October 2013, OPCW officials arrived in Syria to monitor the dismantlement of the Syrian chemical weapons arsenal, after Damascus officially joined the organisation.

The OPCW later said the Syrian government has made its chemical weapon production facilities inoperable.

The dismantlement came after a US-Russian understanding, the first of its kind between the two powers on the Syrian conflict.

Since then, reports of poisonous gas attacks have kept emerging once in a while.