President Donald Trump has reportedly decided to halt the roll-out of sanctions against Russia for its support of Syrian President Bashar al-Assad, contradicting a top diplomat's claims that the sanctions would be announced on Monday.

US Ambassador to the UN Nikki Haley said this weekend that the US would roll out the new sanctions as part of its plan to send a "strong message" about the Assad regime's alleged use of chemical weapons.

On Monday morning, however, White House Press Secretary Sarah Huckabee Sanders said the administration was still considering such a move, and that the decision would be made "in the near future".

The announcement came after Mr Trump told national security advisers he was uncomfortable carrying out the planned sanctions, according to the Washington Post. Administration officials told the Post it was unlikely Mr Trump would approve the sanctions without another "triggering event" by Russia.

A Russian Foreign Ministry official said the Trump administration had assured them shortly after Ms Haley's comments that the sanctions were not coming, according to the Post.

The White House did not immediately respond to a request for comment.

Ms Haley said on Sunday that the sanctions would be implemented shortly, in response to Russian President's continued support of Mr Assad. The US claims Mr Assad used poisonous gas in an attack on the Syrian town of Douma, which is believed to have killed dozens of civilians. The Syrian government and Russia have denied any involvement in the attack.

The US, Britain, and France carried out an air strike on suspected chemical weapons facilities in Syria on Friday. Ms Haley promised a diplomatic response was coming as well.

"You will see that Russian sanctions will be coming down," Ms Haley said on CBS' Face the Nation on Sunday. "[Treasury Secretary Steve] Mnuchin will be announcing those on Monday if he hasn't already, and they will go directly to any sort of companies that were dealing with equipment related to Assad and chemical weapons use."

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She added: "I think everyone is going to feel it at this point. We wanted their friends Iran and Russia to know that we meant business and that they were going to be feeling the pain from this as well."

The comments were met by a harsh rebuke from Russia, which called the proposed sanctions "international economic raiding".

“The sanction campaign against Russia is truly assuming the nature of an obsessive idea,” Kremlin press secretary Dmitry Peskov said, according to Interfax. "...We see them as going against international law.”

The Trump administration decided shortly thereafter to characterise Ms Haley's comments as a misstatement, according to the Post.

The US is testing other diplomatic responses to the situation, including pushing a draft UN resolution that calls for an independent investigation into alleged chemical weapons attacks and identifies those responsible.

The Trump administration also recently expelled 60 Russian diplomats from the US, after the poisoning of a Russian double agent in the UK was tied to Moscow. Russian has denied any involvement in the poisoning.

The US Justice Department and several congressional bodies are currently investigating possible Trump campaign ties to Russia. Mr Trump has denied all allegations of collusion.