The White House and National Security Council did not immediately respond to Anadolu Agency's requests for comment on the report.
Prime Minister Theresa May was holding an emergency cabinet to discuss joining mooted strikes by the U.S. and allies, as rival politicians and some Conservative colleagues called for a parliamentary vote before any British involvement.
Mattis said he personally believes Syria is guilty of an "inexcusable" use of chemical weapons, while noting that the global fact-finding team would likely fall short of determining who was responsible.
"They agreed to keep working closely together on the worldwide response", the statement concluded.
Mattis said Wednesday that the United States is "still assessing the intelligence" on whether the Assad regime is to blame for the recent suspected chemical attack. In another tweet on Thursday, Trump wrote that an attack on Syria "could be very soon or not so soon at all!"More news: Commonwealth Games: 8 Cameroon athletes "abscond"
But rival politicians and some Conservative colleagues have called for a parliamentary vote before any British involvement.
"We will need to take decisions in due course, when we judge it most useful and effective", Macron said. France is already involved in the USA -led coalition created in 2014 to fight the Islamic State group in Syria and Iraq.
The crisis has evoked memories of the Iraq War, when lawmakers approved joining in the face of strong public opposition. A YouGov poll showed just one in five members of the public support a strike on Syria.
Post-World War II Germany typically has been reluctant to engage in military action, and parliamentary approval is required for any military missions overseas.
Formally, the prime minister has the right to go to war without approval from parliament, but a convention has been established in previous conflicts where MPs have a vote either before or shortly after military action begins.More news: PFA Player of the Year shortlist revealed
Parliament voted down British military action against Assad's government in 2013, in an embarrassment for May's predecessor, David Cameron.
But they backed action in Iraq the following year, and again in Syria in 2015, strictly limiting strikes to Islamic State (IS) group targets.
"We continue to consider it extremely important to avoid any steps that could lead to more tension in Syria", Mr Peskov said. That meant airstrikes, possibly in tandem with France and other allies that have expressed outrage at the alleged Syrian chemical attack, could be launched within hours of a presidential decision.
"The position is a very risky one because of Russian involvement, also because we have an erratic president of the United States".
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.More news: Xi defends BRI; says China has no geo-political calculations
"But on a strategic level, it's how do we keep this from escalating out of control - if you get my drift on that", Mattis told the House Armed Services Committee Thursday morning.
- Family of man killed in Tesla auto crash hires law firm
- Weather: Rain in the north, showers and brighter spells in the south
- Oscar-winning director Milos Forman no more
- Here's when the best chance of severe weather will be on Sunday
- Bayern Munich confirm new coach to succeed Heynckes
- Crews battling house fire south of Amarillo, drivers asked to avoid area
- IPL: Roy powers in Delhi victory over Mumbai
- F1: Red Bull's Ricciardo wins Chinese Grand Prix
- Sridevi Wins Best Actress National Award Posthumously for 'Mom'
- Backpage.com pleading guilty to human trafficking charges in Texas