THE diplomatic gulf between Moscow and Washington has been laid bare after Vladimir Putin said relations between the two world powers had been “degraded” while Donald Trump decried Russia for supporting an “animal” in Syria’s Bashar al-Assad.

The barbed language hung over Rex Tillerson, the US Secretary of State’s meeting with his Russian counterpart Sergey Lavrov, and then later with Mr Putin himself. Mr Tillerson acknowledged the two countries had "sharp differences".

Mr Lavrov had made clear the US’s retaliatory strike following last week’s chemical weapons attack in northern Syria was “unlawful” while his deputy, Sergey Ryabkov, denounced the US administration for its “primitive and loutish” rhetoric.

At the United Nations in New York, Matthew Rycroft, the UK ambassador, decried Moscow for siding with a “murderous, barbaric criminal rather than with their international peers”. He insisted: “They have chosen the wrong side of history."

In a strange contrast to the seriousness of the diplomatic impasse, Mr Trump boasted to a TV interviewer about how he had ordered the missile strike in Syria while eating "the most beautiful piece of chocolate cake" during talks with President Xi Jinping of China at his luxury Mar-a-Lago resort in Florida last week.

Given the frosty relations between Russia and America, there was some doubt as to whether or not Mr Putin would meet Mr Tillerson during his visit to the Kremlin. However, a spokeswoman for the US embassy in Moscow, citing Kremlin officials, confirmed it was taking place.

Earlier, the US President expressed anger about the chemical attack on the rebel-held town of Khan Sheikhoun during an interview on the Fox Business Network.

"You see these beautiful kids that are dead in their father's arms or you see kids gasping for life and, you know, it's over for them."

He said he asked his defence minister for options and then added: “We hit them very hard."

Mr Trump claimed Mr Putin was backing a “person that's truly an evil person”. He said it was very bad for Russia, for mankind and the world.

"When you drop gas, or bombs, or barrel bombs - they have these massive barrels with dynamite and they drop them right in the middle of a group of people - and in all fairness, you see the same kids with no arms, no legs, no face. This is an animal."

But he stressed: "Just so you understand, we're not going into Syria."

Meantime, Mr Putin, speaking on Russian television, again rejected allegations that Syria was behind the chemical attack, claiming the country had given up its chemical stockpile.

"Where is the proof that Syrian troops used chemical weapons? There isn't any, he declared.

In New York, Mr Rycroft claimed supporting the Assad regime would result in "shame" and "humiliation" for Russia.

The intensive diplomatic action came as the UN Security Council was set to vote on a draft resolution drawn up by the US, Britain and France calling on the Syrian regime to co-operate with a probe into the chemical weapons attack.

Russia is expected to veto the measure with Alexander Yakovenko, the country's ambassador to the UK, saying: "We don't think that there is any need for such a resolution."

It was expected to condemn the reported use of chemical weapons in northern Syria and demand that all parties provide speedy access for investigators.

It would require the Syrian authorities to provide information about air operations on April 4 when Khan Sheikhoun was attacked, including the names of helicopter squadron commanders, and grant immediate access to air bases.

Speaking at the UN, Mr Rycroft said UK analysis of samples from Khan Sheikhoun had tested positive for the deadly nerve agent Sarin.

Analysis of the samples was carried out by chemical weapons scientists at Porton Down in Wiltshire and tested positive for sarin "or a sarin-like substance".

"The United Kingdom therefore shares the US assessment that it is highly likely that the regime was responsible for a sarin attack on Khan Sheikhoun on April 4," Mr Rycroft said.

The diplomat said the Security Council had been "held to ransom by Russia's shameless support for the Assad regime".

He said: "Time and time again Russia has abused its veto to protect the regime and to defend its use of chemical weapons. And what has Russia got in return for its seven vetoes in six years? Let me tell you.

"Russia's initiative in 2013 to dismantle Syria's chemical weapons has been exposed as a shambles. Russian pride in the Astana process has been turned to humiliation. And Russia's credibility and reputation across the world have been poisoned by its toxic association with Assad.

"They have chosen to side with a murderous, barbaric criminal, rather than with their international peers. They have chosen the wrong side of history."

But Mr Rycroft added that it was not too late for Russia to change course and use its influence over the Assad regime to bring the civil war to an end.