He said that because the United States had no personnel at the site of the suspected chemical attack, it has no hard evidence of what happened, although he personally believed it was an "inexcusable" use of chemical weapons.

The same officials say Syria has continued to produce or procure chlorine, which also has industrial and agricultural uses.

"The Prohibition of Chemical Weapons (OPCW) confirms that the OPCW Fact-Finding Mission (FFM) team is on its way to Syria and will start its work as of Saturday 14 April, 2018", the watchdog said in a statement on Thursday.

Speaking to congress at a hearing of the House Armed Services Committee on Thursday, Mattis said he believed a chemical attack had taken place and blamed Russian Federation for being complicit in Syrian government's possession of chemical weapons.

Photo Vasily A. Nebenzya, the Russian ambassador to the United Nations, exchanged harsh words with the American ambassador at a Security Council meeting on Friday. She told her senior ministers on Thursday the Douma events showed a "deeply concerning" erosion of worldwide legal norms barring the use of chemical weapons.

The UK Cabinet agreed at a meeting on Thursday that Syrian President Bashar Assad's government was highly likely responsible for the alleged chemical attack and that Prime Minister Theresa May should coordinate the response to the incident with the United States and France.

The samples suggested the presence of both chlorine gas and an unnamed nerve agent, two officials said. Trump's ambassador to the United Nations, Nikki Haley, told NBC News on Thursday the administration has "enough proof" of the chemical attack but is still considering its response.

Congress, BJP lock horns, indulge in slugfest over reaction to rapes
An eight-year-old girl from the nomadic Bakerwal Muslim community disappeared near her house on January 10 in Jammu and Kashmir's Kathua district.

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.

At the House hearing, Democrats grilled Mattis on the wisdom and legality of Trump ordering an attack on Syria without explicit authorization from Congress. Mattis argued it would be justified as an act of self-defense, with 2,000 USA ground troops in Syria; he insisted he could not talk about military plans because an attack "is not yet in the offing".

He said even if the investigative team verifies the use of chemical weapons, "we will not know who did it".

Asked about the risks of US military retaliation, Mattis cited two concerns, starting with avoiding civilian casualties. More broadly, he doubted the wisdom of bombing.

President Donald Trump warned Russia Wednesday to "get ready" for a missile attack on its ally Syria. "Not to react is to prove to the rest of the world that what we say does not matter".

Earlier Thursday, Trump appeared to walk back earlier comments in which he warned Russian Federation to brace for missiles which he said "will be coming".