Biological samples from the area of the alleged chemical attack in Syria have tested positive for chlorine and a sarin-like nerve agent, according to a United States official familiar with the United States analysis of the test results.
Trump had vowed to take swift and decisive action against Syria since reports of a suspected poison gas attack on a rebel enclave that killed dozens of people. Russian Foreign Ministry Spokeswoman Maria Zakharova cannot even imagine that either Russian or American blood could be spilt in Syria, she said in an interview with Sky News on Thursday.
Mr. Mattis said he personally believes Syria is guilty of an "inexcusable" use of chemical weapons, while noting that the worldwide fact-finding team would likely fall short of determining who was responsible.
In response, Trump tweeted that while Russian Federation vowed to protect Syria against attack, "Get ready Russian Federation, because [attacks] will be coming, nice and new and "smart!"
During his testimony, Mattis spoke about a possible strike against Syria.
During a Cabinet meeting Thursday morning, the president said, "We are looking very seriously, very closely at that situation and we will see what happens folks. When I leave here, I go to a meeting where the National Security Council will be meeting on this and we will take forward various options to the president".
In London, British Prime Minister Theresa May held an emergency cabinet meeting to discuss support for USA action against the Syrian regime.
Analysts agreed that in striking Syria without U.N. authorization - impossible given Russia's repeated vetoes on the Security Council - the United States, Britain, France were relying instead on a nebulous concept of "legal morality".
But across Western capitals opposition to military action also grew.
"For us, a normalization of chemical weapons use is a threat for our collective security that can not go without a response", a source in Macron's office told AFP.
Mr. Mattis said that although the United States has no hard proof, he believes the Syrian government was responsible for Saturday's attack. Russian Federation and Syria have been calling for the global investigation of the alleged attack. USA lawmakers questioned whether Trump has the legal authority to order strikes without Congressional approval and opposition parties voiced concern.
The OPCW, which works to rid the world of chemical arms stockpiles, said its experts were on their way to Syria and will start their work on Saturday.