Russian experts on the ground have found no evidence of sarin or chlorine use, said Russia's ambassador to the United Nations, who offered Syrian and Russian assistance to allow investigators from the Organisation for the Prohibition of Chemical Weapons to travel to the site.
An American official said the US was discussing with allies whether they would participate in a retaliatory strike.
He added of Russian president Vladimir Putin, "everybody's going to pay a price - he will, everybody will".
In response, Russia's Foreign Ministry said in a Facebook post that "smart missiles should fly towards terrorists, not towards the lawful government".
OPCW establishes a fact-finding mission in response to persistent allegations of chemical weapon attacks in Syria, "to establish facts surrounding allegations of the use of toxic chemicals, reportedly chlorine, for hostile purposes in the Syrian Arab Republic".
Trump was responding to a Russian warning on Tuesday that any US missiles fired at Syria over the assault on a rebel enclave would be shot down and the launch sites targeted.
In Moscow, a senior Russian politician said his country is willing to help arrange a visit this week for experts from the worldwide chemical weapons watchdog to the site of the suspected poison gas attack.
Trump said there was little question that Syria was responsible for the apparent weekend attack, although the government of President Bashar Assad denied it.
USA ambassador Nikki Haley told a closed-door Security Council meeting that the United States wanted a vote on the measure, even though Russian Federation said it contained "some unacceptable elements".
U.S. envoy Nikki Haley said Russian Federation - a Syrian military backer - had the "blood of Syrian children" on its hands and branded President Assad a "monster".
But Russia says it can not support the proposal because it contains "unacceptable elements".
Russian Federation has denied the attack took place or that Moscow or the the Syrian military was involved.
"It's entirely possible that Russian advisers could be present at sites that USA military and allied forces potentially strike", Winnefeld said.
After a deadly sarin gas attack on the rebel-held town of Khan Sheikhun that killed scores of people in April a year ago, Trump quickly ordered a retaliatory strike.
After capturing most of Ghouta, Syria and Russian Federation secured two negotiated withdrawals last month that saw 46 000 rebels and civilians evacuate. The data would refute claims of chemical use, Tass reported.
World Health Organization also cited reports about the deaths of more than 70 people who sheltered in basements, saying 43 of those people who died had shown "symptoms consistent with exposure to highly toxic chemicals".
In a parallel operation, 65 buses carrying fighters and civilians left the outskirts of Ghouta and headed to north Syria, the Syrian Observatory for Human Rights said.
"If there is clear verified evidence of the use of chemical weapons and a proposal for action where the United Kingdom would be useful, then we will look at the range of options", Prime Minister Theresa May's spokesman said.
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