Still, James Jeffrey, a former ambassador to Iraq and deputy national security adviser under George W. Bush, said Trump sounded "very strong against Russian Federation".
The U.S. president had sharply critical words for both Russian Federation and Iran, which have backed Assad's government.
Russian Federation has again denied that a chemical attack was conducted in Syria by showing footage of what it calls the testimony of Syrian residents. Mattis and other government officials from the national security team warned Trump that such action would create conflict with Iran and Russia [VIDEO].
"During the 2000s Russian Federation commenced a programme to test means of delivering chemical warfare agents and to train personnel from special units in the use of these weapons", the letter said.
Russia's UN Ambassador Vassily Nebenzia insisted that there was "no credible confirmation of toxic substance use in Douma", adding that "we have information to believe that what took place is a provocation with the participation of certain countries' intelligence services". But he also appeared anxious to avoid a wider conflict, saying France would "in no way allow an escalation".
Russia, Assad's most important ally in his seven-year-old war with rebels, said it had deployed military police in Douma on Thursday after the town was taken over by government forces. Russia's defence ministry was set to hold a briefing for journalists at around 12300 IST.
One senior official said Trump has asked his military to consider options that would include punishing Russian Federation and Iran - Syria's other main foreign backer - in part over his growing level of exasperation with Putin.
The attack has drawn worldwide outrage and prompted the United States and its allies to consider a military strike on Syria, something Moscow has strongly warned against.
World stocks edged down as anxious investors stayed wary of risky assets.
However, warning of an imminent attack could force U.S. military officials to modify their list of potential targets, which could range from airfields or chemical storage sites to locations in the backyard of Damascus in Assad, according to the message they want to carry.
"A pre-designed scenario is being implemented", Antonov said on Facebook.
Any US strike would probably involve the Navy.
When Ukraine's Kremlin-friendly leader was driven from power in February 2014 by mass protests, Putin reacted to what he described as a US-driven coup by immediately sending troops to overtake Crimea and then annexing the Black Sea peninsula. A USA guided-missile destroyer, the USS Donald Cook, is in the Mediterranean.
The scale of the US -led retaliation on Assad may well determine how Russian Federation responds.
Damascus' allies have condemned US President Donald Trump for ordering air attacks in Syria "on targets associated with chemical weapons capabilities" in collaboration with the United Kingdom and France.
"Insulting the President of Russia is unacceptable and inadmissible", added the envoy, after President Donald Trump directly called out his Russian counterpart Vladimir Putin over his support for the Assad regime.
- No Joel Embiid in Sixers vs Heat Game 1
- Facebook CEO Mark Zuckerberg Made $3 Billion During Hearings
- CBAY) — CymaBay Therapeutics (NASDAQ
- Tesla crash driver's family hires law firm, doubts over autopilot
- No "final decision" yet on Syria response, White House says
- Donald Trump issues full pardon to former aide to Dick Cheney
- USA concerned about triggering wider war as it weighs strike on Syria
- Hearing related to Federal Bureau of Investigation raid at Trump lawyer's office is set
- Mark Zuckerberg's data was collected by third parties
- April 17 last day to file taxes