Now, Syrian president Bashar al-Assad says the chemical attacks that prompted the United States' strike were a "100 percent fabrication".
He continued, "they fabricated the whole story in order to have a pretext for the attack". The U.S. strike, accompanied by hardening American rhetoric on the Syrian president's future, also dragged U.S. relations with his ally, Russia, to their lowest level since the Cold War.
The suspected attack killed at least 87 people, including many children, and images of the dead and of suffering victims provoked global outrage.
"We will keep monitoring the issue, since the only possible reason for using military force on the territory of Syria is to fight terrorism", Lavrov said.
The UK Ministry of Defense and Turkish authorities say they have carried out tests on samples that provide evidence that Sarin or a similar substance was used.
On April 7, the US launched cruise missiles at Syria's Shayrat airfield from which President Donald Trump claimed a chemical weapons attack had been launched. "Even if we have them, we wouldn't use them, and we have never used our chemical arsenal in our history". Russian Federation has alleged that the victims were killed by toxic agents from a rebel chemical arsenal hit by Syrian war planes.
The Syrian government was "highly likely" to have been behind last week's chemical weapons attack, Prime Minister Theresa May has said.
US, Russia: 'Low level of trust'
Even if Assad refrains from the use of chemical weapons, his Russia-supported forces have an enormous upper hand. Washington blames Russia's ally, Syrian President Bashar Assad, while Moscow says Syrian rebels are responsible.
The World Health Organization said last week that some victims showed symptoms consistent with exposure to a category of chemicals that includes nerve agents.
Moscow has warned against putting the blame on Damascus until an independent inquiry is conducted and vetoed a proposed United Nations resolution on the attack, saying it failed to mention the need to inspect the affected area.
"I would like to think that [Russia] didn't know, but certainly they could have", President Donald Trump told reporters at The White House on Wednesday, adding that the Pentagon was still investigating whether Moscow was complicit in the attack.
We don't have any chemical weapons, we gave up our arsenal a few years ago.
It was the 8th time Russian Federation has used its veto power. Publications including in the USA and the United Kingdom have highlighted "many inconsistencies" in the version of events in Syria's Idlib province that was used to justify the American airstrikes, he said.
IS is facing twin offensives by Iraqi forces on the city of Mosul and by an Arab-Kurdish alliance on its de facto Syrian capital Raqa, backed by a US-led coalition that launched air strikes against the jihadists in 2014.