Western powers claim their missile attacks struck at the heart of Syria's chemical weapons program but what they destroyed included a scientific research institution producing cancer drugs.

The Pentagon said three chemical weapons facilities, including a research and development center in Damascus' Barzeh district and two installations near Homs, were hit in the early hours of Saturday.

The Institution for the Development of Pharmaceutical and Chemical Industries, located in the Barzeh neighborhood northeast of the Syrian capital, specialized in producing specific drugs which are direly in short supply amid Western sanctions.

Saeed Saeed, head of the Institution for the Development of Pharmaceutical and Chemical Industries, said the center was previously used by the Organization for the Prohibition of Chemical Weapons (OPCW) but now works on pharmaceutical products.

"Since the Syria crisis broke out, the country has been short of all kinds of medicines due to the sanctions from Western countries. Foreign companies stopped exporting high-quality medicines to Syria, especially anti-cancer medicines. So we have been conducting researches on anti-cancer medicines here, and three cancer drugs have been developed," he said.

Saeed noted that he could not have stayed at the research center after the strikes if it had contained chemical weapons, as claimed by the US and its allies.

"If there were chemical weapons in the building, we would not be here. My colleagues and I came here at 05:00 this morning. If there were chemical weapons, we would need to wear masks and take other protective measures to be staying here," he said.

The fresh strikes by the US marked the second time that President Donald Trump has authorized attacks on Syria.

He ordered a missile strike against Shayrat Airbase in Syria’s Homs Province on April 7, 2017. He claimed back then that the air field had been the origin of a suspected sarin gas attack on the town of Khan Shaykhun in Syria’s Idlib Province on April 4, 2017.

This is while Syria turned over its entire chemical stockpile under a deal negotiated by Russia and the United States back in 2013.

Washington, London and Paris said their aggression was in response to last week's alleged chemical attack in the Damascus suburb town of Douma, which they blamed on the Damascus government.

Syrian air defenses, however, managed to shoot down most of the missiles fired at the country.

Syria's Foreign Ministry strongly denounced Saturday's strikes as a "brutal, barbaric aggression," saying it violated international law and the UN Charter.

The illegal air raids also sparked a wave of condemnations from a number of countries, including Iran, Russia and Iraq.