Sanders says Trump is "confident" in the intelligence related to the attack but she will not specifically say if the US government has determined that Assad's government was behind the attack. "It was an atrocious attack, it was frightful".
Both Damascus and Moscow had warned against using the allegations to justify military action against Assad.
"The Russian regime, whose hands are all covered in the blood of Syrian children, can not be ashamed by pictures of its victims".
The White House deliberations came as Russian Federation and the Syrian military blamed Israel for a pre-dawn missile attack on a major air base in central Syria.
Ms Haley urged the UN to take action, but stressed whether it acts or not "either way, the United States will respond". "Important decisions are being weighed, even as we speak".
British Prime Minister Theresa May called it "reprehensible" and said if the Assad government was found to be responsible, it would be held to account.
The US-sponsored draft "condemns in the strongest terms the continued use of chemical weapons" and also stipulates that measures might be taken against Syria under the UN Charter Chapter 7, which paves the way for the use of force.
"We can't let that happen".
Leaders in France and the United Kingdom have largely adopted the same stance as the US, Nebenzya said.
Mrs May sidestepped a question on whether Parliament would be recalled from recess to debate any military intervention.
Migrant caravan, down by half, soldiers on through Mexico
Caravans like this one are common as an attempt to raise awareness, but they exist apart from the regular flow of migrants. The comments come as Trump has been calling for more military action at the Mexico-U.S. border.
"Through the relevant channels we already conveyed to the United States that armed force under a mendacious pretext against Syria where - at the request of the legitimate government of a country, Russian troops have been deployed - could lead to grave repercussions".
Israel, which has struck Syrian army locations many times in the course of its neighbour's seven-year-old civil war, has not confirmed nor denied mounting the raid yesterday. "We just have to hope that Moscow will not overreact when the strikes come".
"If it's Russian Federation, if it's Syria, if it's Iran, if it's all them together, we'll figure it out and we'll know the answers quite soon", Trump said. Referring to Russian President Vladimir Putin, he added: "Everybody's going to pay a price - he will, everybody will".
"But I think we really need to find out as quickly as we can what the hallmarks of this attack were, and I do believe that we will be able to figure out if it was an attack by the Assad regime", Shea told VOA.
"We are studying that situation extremely closely".
The US State Department said Mr Johnson and his Washington counterpart had discussed "potential further steps the US and United Kingdom governments might take in coordination with other partners".
Syria and its main ally Russian Federation blamed Israel for carrying out an attack on a Syrian air base near Homs on Monday which followed reports of a poison gas attack by President Bashar al-Assad´s forces on a rebel-held town.
Medical workers and rebel fighters in the area have said around 50 people died in the rebel-held town when a helicopter dropped a container of poison gas.
Syria has blamed Israel for a missile attack on a central air base early Monday that reportedly killed 14 people, including three Iranians.
Trump's strike, a year ago, with 59 cruise missiles, on the air base that allegedly launched a sarin gas attack, was supported only because Trump was new in office and the strike was not seen as the beginning of a longer and deeper involvement in a war Americans did not want to fight.
At least 40 people were reported killed in the suspected attack Saturday.