Syrian President Bashar al-Assad's military currently has up to three tonnes of chemical weapons, Israeli defence officials claimed on Wednesday (19 April).

The Organisation for the Prohibition of Chemical Weapons (OPCW), the international chemical weapons watchdog, confirmed the same day that sarin gas or a similar banned nerve agent was used in the 4 April air strikes on Khan Sheikhoun town in Syria's Idlib province.

Israeli defence officials also alleged that the chemical attack was ordered by Syrian military commanders and Assad was aware of the move. However, the Syrian president and as his ally Russia strongly deny the claims.

Nearly 90 people, including several children, died in the attack with many others in critical condition. In retaliation, the US conducted a series of missile strikes on a Syrian air base it suspected of being the launch base for the chemical attack.

Giving the estimate for the first time since the deadly chemical attack on 4 April, an Israeli military official told reporters that Assad still has "between one and three tonnes" of chemical weapons. Two other Israeli defense officials, who spoke on conditions of anonymity, confirmed the assessment, the Associated Press reported.

Bashar al-Assad
An emergency response team attends to a chemical attack victim in Syria
Israeli military revealed that Syrian President Bashar al-Assad (L) is still in possession of up to  three tonne chemical weapons, some of which was allegedly used in the 4 April Khan Sheikhoun chemical attack (R)

In 2013, the Assad regime had disclosed that it had nearly 1,300 tonne chemical weapons, including sarin, VX nerve agent and mustard gas, which are all banned.

The declaration came when the regime pledged to destroy its weapons cache to prevent US strikes in retaliation of a Syrian chemical attack on Damascus in August 2013, widely believed to have been carried out by Assad's forces, though the regime denies responsibility. The attack had also led to global outrage against Assad after hundreds of innocent civilians died in the then rebel-held area.

It was reported at the time that the entire stockpile was dismantled and shipped out of the country under international supervision in 2014, and was later destroyed.

However, there were doubts that the regime had handed over all the chemical weapons it possessed and a belief that it did not declare all of its production facilities, some of which are feared to have been taken over by Isis.

Meanwhile, Dan Kaszeta, a UK-based chemical weapons expert, told the AP that the Israeli estimate of Assad's chemical weapons cache appeared to be conservative, yet it was enough to be highly lethal.

"One tonne of sarin could easily be used to perpetrate an attack on the scale of the 2013 attack," he explained, adding: "It could also be used for roughly 10 attacks of a similar size to the recent Khan Sheikhoun attack."