As the administration prepares a counter response to the latest attack, which appeared to target civilians and young children, Mr. Trump warned in a tweet Wednesday morning that some sort of missile strike was forthcoming.
So far none of the Security council meetings over the issue has yielded result.
Mattis said options would be discussed with Trump at a meeting of his National Security Council on Thursday afternoon.
Speaking about the Skripal poisoning and looming decision over air strikes against the Syrian government, he accused humanitarian groups of staging the chemical attack and blasted the United Kingdom for a lack of "transparency" during the Salisbury investigation.
The US State Department said the United States has proof at "a very high level of confidence" that the Syrian government carried out the attack but is still working to identify the mix of chemicals used.
This is a big change from Trump yesterday telling Russian Federation to "get ready", but while cooler heads might be getting at least some hearing at these meetings, there's still no guarantee they will ultimately prevail.
"These can be not only American securities... but also a whole range of other goods that are delivered to the Russian market or produced by American businesses on the territory of our country", Medvedev said, answering questions from the Russian State Duma on Wednesday.
The Russian Foreign Ministry also claimed that following Syrian rebels' withdrawal from the eastern Ghouta suburbs of Damascus, stockpiles of chemical agents were allegedly found there. "We hope there will be no point of no return".
"The intelligence provided certainly paints a different picture", Sanders said.
Erdogan said he'll talk to Putin later on Thursday, a day after he talked to President Donald Trump about Syria. "So the situation is very risky".
Mattis' remarks at a House Armed Services Committee hearing followed a series of Trump tweets this week that initially indicated he was committed to bombing Syria but later suggested he was awaiting further advice and assessment. Get ready Russian Federation, because they will be coming, nice and new and "smart!", he threatened.
Air disaster in Algeria, over 100 killed
Some of the victims of that crash were civilians as military dependents often used the planes to travel as well as troops. One farmer said some passengers jumped out of the aircraft sooner than the crash , in response to the Related Press.
Mattis disclosed that the US had not yet confirmed that the Douma attack - the most recent suspected Syrian chemical weapons attack, on April 7 - included the use of sarin gas. Stop the arms race?
Trump chastised Russian Federation and Iran for supporting "murderous dictators", and noted that Putin had guaranteed a 2013 worldwide agreement for Assad to get rid of all of his chemical weapons.
"500 people were poisoned in Syrian 'chemical attack".
In Paris, President Emmanuel Macron said in a statement, "The red line set by France in May 2017 has been crossed". "We're going to cover it in gas and burn it together with an American flag", he promised. The Syrian authorities said they would open all gates for them.
Speaking to reporters in Moscow, Lavrov reiterated a strong warning to the West against military action in Syria.
The response may not be military, but it should extract some sort of cost - whether political, military or economic - each time, Hersman said.
Senior US military sources say President Assad's forces have already moved some aircraft in an attempt to protect them from attacks.
"We will need to take decisions in due course, when we judge it most useful and effective", Macron said.
"France will not allow any escalation that could harm stability in the region", he added.
Activists, rescue workers and medics say dozens of people died in the rebel-held town of Douma on Saturday.
At stake in Syria is the potential for confrontation, if not outright conflict, between the US and Russian Federation, former Cold War foes whose relations have deteriorated in recent years over Moscow's intervention in Ukraine, its interference in the 2016 USA presidential election and, most recently, its support for Syrian President Bashar Assad. The ministry also pointed at previous use of chemicals by the rebels in fighting with Syrian government troops.