US President Donald Trump holds Russia and Syria responsible for a suspected chemical attack that killed more than 40 people, the White House said on Wednesday, refusing to rule out direct military engagement with Russia. 

White House Press Secretary Sarah Sanders slapped aside Russian suggestions that Saturday's attack in Douma could have been faked and said Trump was still weighing military options in response. 

"The intelligence provided certainly paints a different picture," she said of the Kremlin's theory. "The president holds Syria and Russia responsible for this chemical weapons attack." 

An image grab taken from a video released by the Douma City Coordination Committee shows unidentified volunteers spraying a man with water at a make-shift hospital following an alleged chemical attack on Douma, Syria, April 7, 2018. /VCG Photo

Trump is believed to be considering standoff missile strikes against facilities related to the production and delivery of chlorine and sarin or sarin-like agents. But many of Syria's most sensitive military facilities are protected by Russian missile defense systems or are located at bases where Russian, Iranian and Syrian personnel cohabit. 

Sanders pointedly refused to rule out the possibility of direct military engagement with Russia. "Once again, all options are on the table," she said. 

Still, despite Trump's tweets early Wednesday that promised "nice and new and 'smart!'" missiles were headed for Syria, Sanders said no "final decisions have not been made on that front." 

Moscow is in direct contact with the US Joint Chiefs of Staff about the situation in Syria, Vladimir Shamanov, head of the lower house of the Russian parliament's defense committee, told the Interfax news agency on Wednesday.

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Missiles 'will be coming'

"Russia vows to shoot down any and all missiles fired at Syria. Get ready Russia, because they will be coming, nice and new and 'smart!'" Trump tweeted on Wednesday morning.

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Syria later comdemned the threats as a "reckless escalation," state news agency SANA said.

"We are not surprised by such a reckless escalation from a regime like the United States which has fostered and continues to foster terrorism in Syria," SANA reported an official source at the foreign ministry as saying.

Russian foreign ministry spokeswoman Maria Zakharova said in a Facebook post, responding to Trump's twitter: "Smart rockets should be aimed at terrorists, rather than the legitimate government, which has for several years been fighting international terrorism on its territory." 

The Kremlin earlier on Wednesday also urged restraint in Syria, saying that countries should avoid taking action that could further destabilize the war-torn country, as the US considered missile strikes over alleged chemical attacks.

"As before we would hope that all sides will avoid steps that in reality are not provoked by anything and that could destabilize the already fragile situation in the region," Kremlin spokesman Dmitry Peskov told journalists.

"The situation is tense," Peskov said, adding that Russia is calling for an "unprejudiced and objective investigation before making judgments" on the suspected use of chemical weapons.

Members of the UN Security Council vote on the third draft resolution to create a new inquiry to find blame for the chemical weapons attack last week in Douma, Syria, during a United Nations Security Council meeting, in New York City, April 10, 2018. /VCG Photo‍

Russia on Tuesday at the United Nations Security Council vetoed a US-drafted resolution on setting up a panel to identify the perpetrators of toxic gas attacks after chemical weapons were allegedly used in the rebel-held town of Douma.

Russia has said its military specialists found no evidence of a chemical attack on Saturday in Douma and suggested that rebels staged or spread rumors of an attack to pin the blame on Damascus.