Russia has accused the US of "primitive and loutish rhetoric" as talks between top officials get underway
US President Donald Trump's administration has accused Russia of trying to shield the Syrian government from blame for last week's deadly gas attack in the country.
A White House report shown to reporters said Syrian planes were in the vicinity of the chemical attack site about 20 minutes before the attack – and left shortly afterward.
As the four-page document was released, one White House official told Reuters it is, “clear that the Russians are trying to cover up what happened there.”
Meanwhile, as talks got underway between the two country's top officials in Moscow, Russia's deputy foreign minister accused the US of "primitive and loutish" rhetoric over Syria.
Sergei Ryabkov also said Washington's position on the six-year conflict remains a "mystery."
US Secretary of State Rex Tillerson is meeting with his Russian counterpart Sergei Lavrov this afternoon to discuss the chemical attack and America's missile strike response.
A spokesperson for the Kremlin said "there is a certain possibility" that he may also meet Russian President Vladimir Putin later.
As the talks got underway, Mr Lavrov reaffirmed Russia’s position that the missile strikes were unlawful and in contravention of the UN charter.
He said he expected to hold frank and honest discussions with Tillerson on a unified response to terrorism – but added that it was important not to allow a repeat of the US intervention.
The Trump administration has said that the attack was in retaliation for a chemical attack in Idlib province widely blamed on the Syrian President Bashar al Assad.
US intelligence indicates that the chemical agent in the attack was delivered by Syrian Su-22 aircraft that took off from the Shayrat airfield.
On Tuesday, the US ambassador to the UN, Nikki Haley, said she thought Russia knew about the chemical attack in advance.
"They didn’t look shocked,” she said on CNN. “They didn’t look surprised.”
“They were so quick to defend. And then the evidence comes out, and we see exactly what it is and we know exactly what the environment was. Then you realize."
In opening comments as they gathered surrounded by officials, Mr Lavrov he wanted to know the White House's "real intentions" in intervening in Syria - but also promised that Russia was ready for constructive dialogue.
Mr Tillerson is believed to be hoping to convince the Kremlin to change or tone down its support for Syria President Assad.
The US Secretary of State told Mr Lavrov he wanted to clarify areas of common interest and see if they could narrow their differences.
Mr Tillerson has accused Russia of "failing" to uphold its 2013 commitment to ensure the Syrian regime gives up its chemical arsenal.
"It is unclear whether Russia failed to take this obligations seriously, or Russia has been competent," he said in comments earlier this week.
The two men are now holding talks behind closed doors, before a joint news conference later.
Mr Tillerson's visit is the first time a senior Trump official has visited Russia.
The tension is a far cry from his days visiting the country as the boss of oil giant ExxonMobil, when Mr Putin awarded him the Order of Friendship.
Hopes of Mr Tillerson fronting up to Russia with the threat of new sanctions were blocked by other G7 ministers at a meeting in Italy on Tuesday.
British Foreign Secretary Boris Johnson had championed the idea but it was blocked by the Germany, Italy and France.
Additional reporting from IRN ...