The Kremlin on Tuesday accused Washington of refusing to face up to reality over an alleged chemical attack on a rebel-held town in Syria, for which Moscow insists there is no evidence.
"You see the unconstructive position that some countries including the US have taken. They are a priori refusing to face reality," Kremlin spokesman Dmitry Peskov told journalists.
He added that "none of them is talking about the need for an unbiased investigation" and said that this limited the diplomatic options for Russia, but that it would continue "active work on the diplomatic front."
Peskov spoke after US President Donald Trump on Monday said the apparent chemical weapons attack would be "met forcefully" and indicated a decision on military action was hours away.
The Kremlin spokesman said that there was as yet no agreement on the date for a proposed meeting between Trump and Vladimir Putin.
Russia's UN ambassador on Monday warned that the use of military force against Syria could have "grave repercussions."
The Russian defence ministry dismissed footage of attack victims as "yet another fake," following Moscow's practice of suggesting that rebels are staging attacks to discredit President Bashar al-Assad's regime, which Russia supports militarily.
The defence ministry said its specialists visited hospitals in Douma, the largest town in the Eastern Ghouta region outside Damascus, but found no evidence of a chemical attack.
Deputy foreign minister Mikhail Bogdanov on Tuesday said that "fabrications and false stories are being used to find some pretext for the use of military force," RIA Novosti news agency reported.
"We consider this absolutely unacceptable and extremely dangerous," Bogdanov said.