Assad 'would be ill-advised ever again to use chemical weapons,' US Defence Secretary says

Strong rhetoric comes just days after Russia and Iran warned the US they would 'respond with force' if their own 'red lines' were crossed

US Defence Secretary James Mattis (REUTERS)

Bashar al-Assad's Syrian government "would be ill-advised ever again to use chemical weapons," US Defence Secretary James Mattis has said.

In a statement addressing last week's cruise missile strike on Sharyat airfield, General Mattis called it a "measured response to the Syrian government's use of chemical weapons". The strike damaged or destroyed a fifth of Syria's operation aircraft, he claimed.

He added: "The President directed this action to deter future use of chemical weapons and to show the United States will not passively stand by while Assad murders innocent people with chemical weapons, which are prohibited by international law and which were declared destroyed.

"The Syrian government would be ill-advised ever again to use chemical weapons."

A senior US official told the Associated Press the US had concluded that Russia knew in advance of Syria's plans for the attack on Khan Sheikhoun.

Gen Mattis' strong rhetoric comes just days after Russia and Iran warned the US they would "respond with force" if their own "red lines" were crossed in Syria.

"What America waged in an aggression on Syria is a crossing of red lines. From now on we will respond with force to any aggressor or any breach of red lines from whoever it is and America knows our ability to respond well," the joint command centre for powers allied with Mr Assad said.

Gen Mattis added: "The assessment of the Department of Defence is that that strike resulted in the damage or destruction of fuel and ammunition sites, air defence capabilities, and 20 percent of Syria's operational aircraft.

"The Syrian government has lost the ability to refuel or rearm aircraft at Sharyat airfield and at this point, use of the runway is of idle military interest."

After the chemical attack, Damascus claimed it destroyed its toxic stockpiles following an international agreement struck in 2013.

The Russian defence ministry put out a competing version of events claiming legitimate Syrian air strikes against “terrorists” had struck a warehouse used to produce and store shells containing toxic gas, which were allegedly being sent to Iraq.

The joint command centre also said on Sunday the missile strike would not deter it from “liberating” Syria, and that the US military presence in the north of the country amounted to an illegal “occupation”.

Mr Putin and Iranian leader Hassan Rouhani have called for an objective investigation into the chemical attack.