"It has been our consistent position that the use of chemical weapons by anyone, anywhere under any circumstances should not happen", he said.
Syrian President Bashar al-Assad has dismissed reports of last week's chemical attack as "100% fabrication", an assertion at odds with numerous eyewitness accounts, independent analysis and even the explanation given by its strongest ally, Russia.
Speaking to AFP news agency, the president added that the peace talks on resolving his country's war were ineffective because Washington was "not serious" about ending the conflict.
But Assad said it was possible to fake video and suggested the whole incident had been staged.
This time, the military statement said that the terrorist groups, including IS and the al-Qaida-linked Nusra Front are in possession of chemical weapons.
Mansour's brother, Osama was killed in a gunbattle with security forces in northern Lebanon in 2015.
U.S. Ambassador to the U.N. Nikki Haley said the veto left Moscow, a key ally of the Syrian government, with "a lot to prove".
Secretary of State Rex Tillerson said in Moscow Wednesday that the U.S.is confident of its conclusion that Syrian government forces were behind the attack.
Russia's Foreign Minister Sergei Lavrov said Thursday he and Tillerson had discussed the United States strike and agreed "such a situation should not be repeated".
The war also led to the emergence of the Islamic State jihadist group, which seized control of large parts of Syria and Iraq in 2014 but has since lost much of the territory it once controlled.
He said his forces had not been diminished by the United States strike.
British scientists have said a toxic gas known as sarin was used in the attack on a rebel-held town, she said.
A handout picture released by the Syrian presidency's press office shows Syrian President Bashar al-Assad during an interview with AFP in the capital Damascus, on April 12, 2017.
The chemical attack also invited deadly US air strike on the Shayrat airfield of the Syrian air forces, believed by Washington to be the base for warplanes that carried out the chemical attack.
Assad said he would only allow an "impartial" external investigation involving "unbiased countries", according to AFP.
United Kingdom analysis of samples from the Syria chemical attack has detected sarin or a sarin-like substance, Britain's UN ambassador has said.
The mission's findings are expected to be be reported in three weeks.
"Syria emphasizes its willingness to provide the mission access to Shayrat airbase to determine whether sarin was stored there", the diplomat said.
US Central Command said coalition aircraft were given the wrong co-ordinates by their partner forces, the predominantly-Kurdish Syrian Democratic Forces (SDF), for a strike meant to target Islamic State militants south of their Tabqa stronghold, near the extremists' de facto capital, Raqqa. "They want to use it as an umbrella for the terrorists", Assad said. An estimated 300,000 people are in the city. Assad keep on saying that these attacks were useless.