Beirut: Syrian President Bashar al-Assad has broken his silence over a deadly chemical weapons attack that killed scores of civilians, describing it as a "fabrication" to justify American military action.

In a combative Agence France-Presse interview subject to strict restrictions by the Syrian regime, Dr Assad dismissed photographs and video footage that moved President Donald Trump to launch retaliatory strikes on a Syrian air base. He insisted that his government would never use banned weapons.

"Our impression is that the West, mainly the United States, is hand in glove with the terrorists," Dr Assad told the news agency. "They fabricated the whole story in order to have a pretext for the attack."

The comments were Dr Assad's fullest since the April 4 chemical assault on the north-western town of Khan Sheikhoun. According to victims, rescue workers and monitoring groups, it took place shortly after 6am, killing more than 80 people and causing hundreds more to convulse, choke and foam at the mouth.

According to CNN, strict restrictions were placed on AFP in order to be granted the interview: "It was not allowed to film the interview itself; instead, the encounter was filmed by the Syrian presidency. Only footage of first five questions asked by the interviewer was provided to AFP."

The attack, which US officials believe took place with the knowledge of high-ranking Syrian government officials, prompted Mr Trump to launch the US military's first direct assault on an Assad-linked target since Syria's war began six years ago. The US strike, accompanied by hardening American rhetoric on the Syrian president's future, also dragged US relations with his ally, Russia, to their lowest level since the Cold War.

But Dr Assad said evidence collected at the scene came only from "a branch of al-Qaeda", referring to a former jihadist affiliate that is among the groups controlling Idlib province, where Khan Sheikhoun is located.

It was the Syrian government's second version of events in the space of nine days. In earlier comments, officials attributed the deaths to a Syrian airstrike that hit a rebel factory where chemical weapons were being made, releasing the toxins.

"There was no order to make any attack. We don't have any chemical weapons. We gave up our arsenal a few years ago," Dr Assad said. "Even if we have them, we wouldn't use them, and we have never used our chemical arsenal in our history."

The Syrian government was supposed to have given up its entire chemical weapons stockpile under the terms of a 2013 deal brokered by Russia and the United States.

"Frankly, that didn't happen," a Western diplomat said this week, speaking on condition of anonymity.

Activists and monitoring groups have continued to record chemical weapons attacks on opposition-held areas. According to the Syrian Network for Human Rights, Syrian government warplanes have used chlorine gas on opposition-held territory on nine separate occasions this year.

The Organisation for the Prohibition of Chemical Weapons (OPCW) has begun an investigation into the alleged attack, but Russia on Wednesday blocked a UN Security Council resolution demanding that Syria cooperate with the probe.

British Prime Minister Theresa May said on Thursday that Britain believed Dr Assad's government was responsible, despite his rejection of culpability.

"We believe it is highly likely that the attack was carried out by the Assad regime," Mrs May said in a televised statement. "Apart from anything else, we believe it's only the regime that has the capability to make such an attack."

Samples taken from Khan Sheikhoun last week tested positive for the nerve agent sarin, the British delegation at the global chemical weapons watchdog OPCW said on Thursday. 

US denies hitting poison gas depot

The US-led coalition against Islamic State on Thursday denied a Syrian army report it had carried out an air strike that had hit poison gas supplies belonging to IS and caused the deaths of hundreds of people.

A statement by the Syrian army, circulated by state media, said the alleged incident late on Wednesday in the eastern Deir al-Zor province proved that Islamic State and al Qaeda-linked militants "possess chemical weapons". 

Responding to Thursday's Syrian army claim, US Air Force Colonel John Dorrian, a spokesman for the coalition, said it had carried out no air strikes in the area of Deir al-Zor at the time.

"The Syrian claim is incorrect and likely intentional misinformation," Colonel Dorrian said in an email to Reuters.

The Russian defence ministry said it had no information about people killed in an attack by international coalition forces in Deir al-Zor, according to RIA news agency. A ministry spokesman said Russian forces had sent drones to check the area.

Reuters