"As the President noted on April 8, the chemical weapons attack by the Syrian regime against innocent civilians in Duma, Syria on April 7 was horrifying, and demands an immediate response from the global community", he added.
The drumbeat of military action appeared to grow louder, as Russian Federation stonewalled diplomatic efforts at the United Nations and France declared "proof" that Moscow's Syrian ally carried out a deadly chemical weapons attack that killed more than 40 Syrians.
Russian lawmakers have warned the United States that Moscow would view an airstrike on Syria as a war crime and that it could trigger a direct U.S-Russian military clash. "You shouldn't be partners with a Gas Killing Animal who kills his people and enjoys it!"
Trump suggested Monday he had little doubt that Syria was to blame, but neither he nor other administration officials have produced hard evidence. Initial reports indicated the use of chlorine gas, possibly in addition to the nerve agent Sarin.
In the past, Trump has condemned others for forecasting military plans, repeatedly blistering President Barack Obama during the 2016 campaign. We are totally predictable.
Trump has never been skeptical of war, but he seeks to avoid regime change projects because his nationalist agenda has no place for the cost and responsibility of foreign nation-building (and, in recent years, cycles of insurgency, military surge, and reconstruction) they inevitably incur.
Rep. Adam Smith, the ranking Democrat on the House Armed Services Committee, said he sees no legal justification for a US strike in Syria, absent explicit authorization by Congress. US officials have been consulting with France, Britain and other allies on a possible joint military operation, but the timing remained in doubt Wednesday.
Shortly after his tweeted warning to Russia, Trump took a more conciliatory tone in lamenting that the U.S. -Russia relationship "is worse now than it has ever been". "So we're looking at that very strongly and very seriously".
Britain's government weighed the possibility of military action against Syria on Thursday but faced growing scepticism from opposition leaders and deeper divisions in a country still haunted by its role in the US-led invasion of Iraq.
President Vladimir Putin said on Wednesday that he hoped common sense would prevail and that the situation would stabilise.
Trump is slated to speak with French President Emmanuel Macron and British Prime Minister Theresa May Thursday evening.
Russian military police have started patrolling the site of last weekend's alleged chemical attack in Syria.
The U.S., France and Britain have been consulting about launching a military strike. After lauding global cooperation in a United Nations speech a year ago, Macron now finds himself planning a military attack without a UN mandate - hence his need for allies.
France already has some 1,100 troops involved in its Operation Chammal, created in 2014 to fight Islamic State extremists in Iraq and extended in 2015 to Syria, as part of the US -led coalition. Multiple IS terror attacks have targeted France, including one last month.