Defense Secretary Jim Mattis said Tuesday that the United States is not trying to get involved in Syria's civil war, but the US would hit Syrian government targets again if Assad used chemical weapons again.
Trump said, "I would like to think that they didn't know, but certainly they could have. But it doesn't have to be this way".
Russian Federation imposed its veto as US Secretary of State Rex Tillerson said after talks in Moscow that there was a "low level of trust" between the United States and Russian Federation.
Ten countries voted in favour of the text, while Bolivia joined Russian Federation in voting no.
Damascus and Moscow claim the toxic gas that killed dozens of civilians in a rebel-held Syrian town on April 4 was released when government bombs struck a rebel-controlled chemical weapons depot - an assertion that Western governments reject.
Russian Federation says rebels were responsible for whatever chemical agent was found, which the Trump administration calls a disinformation campaign. "But when I see people using awful, terrible chemical weapons, which they agreed not to use under the Obama administration, but they violated it", he said, explaining the strike.
U.S. Ambassador Nikki Haley told the council: "We want to work with Russian Federation to advance a political process in Syria".
U.S. Central Command said Thursday that coalition aircraft were given the wrong coordinates by their partner forces, the predominantly-Kurdish Syrian Democratic Forces, for a strike meant to target Islamic State militants south of their Tabqa stronghold.
The news conference came after Russian President Vladimir Putin met the top American diplomat for nearly two hours to see if they could rescue relations between the world's mightiest military powers.
"We had a lengthy exchange of views regarding the situation in Syria and shared perspectives on possible ways forward", Tillerson said.
"Unfortunately, we've got some differences with regards to a majority of those issues", Lavrov lamented. "How do you know that?" he said. USA officials have said that there is "no doubt" that Syrian President Bashar al-Assad is responsible for the attack.
And so, on Wednesday, Mr. Putin could keep Mr. Tillerson waiting and wondering whether he would find time in his schedule to meet the top American diplomat.
Mr Trump said Mr Tillerson had completed a successful meeting with Mr Putin, where "things went pretty well".
After a campaign marked by friendly comments about Russia, President Donald Trump sounded a different note on Wednesday about the current state of U.S. -Russia affairs.
White House officials said Wednesday that there is credible evidence pointing to Russian interference in Montenegro's election last October.
Trump and others have indeed threatened similar action.
Boris Johnson has urged Russian Federation to stop "acting as a lifeline for Assad's murderous regime" in Syria and instead to "live up to its responsibilities as a global power".
"People, not just in the West but across the Middle East and the world are speaking out against Assad's brutality", she said. "Things will work out fine between the United States of America and Russian Federation", he tweeted.
The decision by the United States to strike Assad's air base broke with its stated mission under Operation Inherent Resolve that US and coalition forces are only in Syria to defeat the Islamic State there.