Russian President Vladimir Putin has said Russia holds information that the US is planning to launch new missile strikes on Syria, and there were plans for the US to fake chemical weapons attacks there.
Mr Putin said Russia would tolerate western criticism of its role in Syria, but hoped that attitudes would eventually soften.
"We have information that a similar provocation is being prepared in other parts of Syria including in southern Damascus suburbs where they are planning to again plant some substance and accuse the Syrian authorities of using chemical weapons."
He did not offer any proof for that assertion.
However, a White House official said there is no evidence to support Russian claims that the chemical attack in Idlib, Syria, was fabricated.
The official said the mass of data they have "in all the different vehicles we've gotten it is just too massive for any intelligence organisation to fabricate in that short a period of time".
Turkey's health minister Recep Akdag has also confirmed to a state-run news agency the use of sarin gas in the Syrian chemical attack.
Mr Akdag said isopropyl methylphosphonic acid had been identified in blood and urine tests conducted on samples taken from victims exposed to chemical warfare.
The acid is formed from a byproduct of sarin reacting with other compounds.
Both Washington and Ankara blame the Syrian government for the chemical attack which killed nearly 100 people including children, but Damascus has denied responsibility.
The US launched missile strikes last week against a Syrian government air base in response.