The Russian prime minister has denounced Washington’s missile attack on a Syrian military airbase earlier this month, saying the strike gave the Daesh Takfiri terrorist group free rein to continue its terror campaign.

Dmitry Medvedev made the remarks in an address to the State Duma, the lower house of the parliament, in Moscow on Wednesday.

He stressed that the April 7 US missile strike against Shayrat Airfield in Syria’s Homs province was "an act of military aggression" as it was not authorized by the United Nations and violated international law.

"We do not know what may happen next. But I know for sure who benefited from this act of aggression — Daesh, because [the attack] gave them [terrorists] a free rein," he said.

The Russian premier further accused the US administration of fighting the Damascus government instead of terrorism.

“Whether Americans like it or not,... that (the Syrian leadership) is a legal political power," he added.

Medvedev also warned that further escalation of the conflict gripping Syria would result in “the destruction of the Syrian state, its disintegration and a partial victory of terrorists.”

Washington claimed that Shayrat Airfield had been used to conduct what it said was a chemical attack on the town of Khan Shaykhun in Syria’s Idlib province on April 4. Over 80 people were killed in the town due to the attack

The West held Damascus responsible for the purported gas attack, but Syria denied the accusation and stressed that the casualties in Khan Shaykhun were caused when a conventional airstrike hit a depot where militants stored chemical weapons.

'Well-planned provocation'

Elsewhere in his comments, Medvedev said that what happened in Khan Shaykhun was a "well-planned provocation from which, probably, the US administration benefited." 

He also called for a thorough investigation into the incident and warned against pointing the finger of blame at the government of Syrian President Bashar al-Assad.

Syria has faced foreign-sponsored militancy since 2011. Damascus has repeatedly accused Saudi Arabia, Qatar, and Turkey of providing the militants with banned weapons.

Syria gave up its entire arsenal of chemical arms under a deal reached between the US and Russia in 2013.