UN Security Council to vote Tuesday on Syria sanctions
Russia has vowed to use its veto to block the measure, which would be the seventh time that Moscow has resorted to its veto power to shield its Damascus ally.
The vote scheduled for 11:30 am (1630 GMT) would mark the first major council action by the new US administration of President Donald Trump, who is seeking warmer ties with Russia.
US Ambassador Nikki Haley was in Washington on Monday to join Trump and Vice President Mike Pence for a White House lunch, with foreign policy expected to be a focus of discussion.
"How much longer is Russia going to continue to babysit and make excuses for the Syrian regime?" she said on Friday following a closed-door council meeting to discuss chemical weapons use in Syria.
"People have died by being suffocated to death. That's barbaric."
The proposed resolution drafted by the United States, Britain and France would slap sanctions on 11 Syrian nationals and 10 entities linked to chemical attacks in the nearly six-year war.
It would also ban the sale, supply or transfer of helicopters and related materiel, including spare parts, to the Syrian armed forces or the government.
The proposals follows a UN-led investigation which concluded in October that the Syrian air force had dropped chlorine barrel-bombs from helicopters on three opposition-held villages in 2014 and 2015.
The joint panel of the United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) also found that Islamic State extremists had used mustard gas in an attack in 2015.
Russian Deputy Ambassador Vladimir Safronkov said on Friday that Moscow would veto the measure because it was "one-sided" and based on "insufficient proof."
A recent report by Human Rights Watch showed that Syrian regime forces carried out at least eight chemical attacks during the final weeks of the battle for Aleppo, killing nine people and injuring hundreds more.
The Syrian regime has repeatedly denied using chemical weapons in the war that has killed 310,000 people since March 2011.