Washington: The US Defence Department has said airstrikes on Syria had struck all of their targets and none of the coalition's planes or ship-launched missiles had been intercepted by President Bashar al-Assad's forces.

Pentagon spokeswoman Dana White and US Marine Lt. Gen. Kenneth F. McKenzie Jr. made the remarks during a news briefing on Saturday, describing an early Saturday morning operation carried out jointly by the US, UK and France in retaliation for an alleged chemical weapons attack last weekend on a then-rebel-held town near Damascus, Efe news reported.

"This operation was carefully orchestrated and methodically planned to minimize potential collateral damage... We successfully hit every target," White said.

She said that unlike the airstrikes carried out in April 2017 against Assad, when the US targeted Syria's Shayrat Airbase in Homs in retaliation for a chemical attack on Khan Shaykhun, a town in the northwestern province of Idlib, the latest airstrikes were aimed at neutralizing chemical weapons research and development facilities.

"This operation does not represent a change in US policy, nor an attempt to depose the Syrian regime. These strikes were a justified, legitimate and proportionate response to the Syrian regime's continued use of chemical weapons on its own people," White said.

For his part, McKenzie said three facilities that "were fundamental components of the regime's chemical weapons warfare infrastructure" had been targeted.

The US Defense Department said in an earlier news release that the first airstrike targeted a scientific research center in the greater Damascus area that was being used to research, develop, produce and test chemical and biological agents. McKenzie said 76 missiles were used in that strike.

It said a second airstrike by the US and its allies destroyed a warehouse west of the western city of Homs, where Assad's government was storing its main reserves of sarin gas, one of the substances purportedly used in the alleged chemical attacks.

A third airstrike targeted a storage site for chemical weapons equipment and a command post, both of which also were located near Homs.

"None of our aircraft or missiles involved in this operation were successfully engaged by Syrian air defenses, and we have no indication that Russian air defense systems were deployed," McKenzie said.

US President Donald Trump on Saturday morning thanked France and the UK for their participation in the airstrikes against positions of Assad's government, which has been engaged in a seven-year-old civil war against rebel groups and is backed by Russia and Shia militias.

"A perfectly executed strike last night. Thank you to France and the United Kingdom for their wisdom and the power of their fine Military. Could not have had a better result. Mission Accomplished!" Donald Trump wrote on Twitter.

The airstrikes were carried out in retaliation for an alleged chemical weapons attack on April 7 by Syrian government forces on the then-rebel-held town of Douma, located in the Eastern Ghouta region just east of Damascus.

More than 43 people who showed "signs and symptoms consistent with exposure to toxic chemicals" died in Douma, according to the World Health Organization (WHO).

The Syrian Observatory for Human Rights, a London-based monitoring group, said in a statement on Saturday that Syrian government troops and their allies had taken-up positions inside Douma and now have complete control over the area.

Syria and Russia deny that any chemical attack occurred and say the incident was staged by foreign intelligence services so it could be used as a pretext for military action against Assad.