But his call was wrapped in kind words about the Syrian president and condemnation of the USA strikes carried out on a Syrian airbase on Friday, in retaliation for a chemical attack on civilians in a rebel-held area of Syria.
President Donald Trump's military attack on the Assad regime was, in itself, a stark reversal from his earlier position to work with Russia, Syria's key ally, to negotiate a solution to the country's civil war. He also said the top USA priority in the region hasn't changed and remained the defeat of Islamic State militants.
Nikki Haley's comments in an interview airing Sunday came as part of an apparent shift in U.S. policy towards Assad's government after the alleged chemical attack last week on the rebel-held town of Khan Sheikhun that killed 87 people, including many children. Haley said she doesn't see a political solution in Syria with Assad remaining as president, but that other USA priorities were defeating Islamic State and to "get the Iranian influence out".
"We've seen what that looks like, when you undertake a violent regime change in Libya, and the situation in Libya continues to be very chaotic", he said.
"We are asking Russian Federation to fulfill its commitment and we're asking and calling on Bashar al-Assad to cease the use of these weapons".
Syria's President Bashar al-Assad..
Before the Khan Sheikhun attack, Tillerson said Assad's fate should be decided by the Syrian people, suggesting Washington would not oppose him standing for reelection. The Syrian government has denied it was behind the attack.
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Another airstrike came in the northwest Syria town of Urom al-Joz, where 18 people were slain - including five children and two women, and another Saturday bombing by the USA -led coalition killed at least 21 people, including a woman and her six kids on a boat in the Euphrates River, according to activists.
On Saturday, two Syrian opposition-held towns, including the one where 87 people died in the chemical weapons attack, were hit by deadly airstrikes.
Days later, after a chemical weapons attack on Syrian civilians that the USA blames on Assad's regime, the Trump administration sharpened its rhetoric and launched several dozen cruise missiles at a Syrian airfield, marking the first US military effort against the Assad government.
Pressing Lavrov on Russia's failure to eliminate Syria's chemical weapons stockpile is likely to be part of the agenda.
Moscow has said it doesn't believe Assad's forces carried out the attack on Thursday that involved children and called for a "thorough and impartial" investigation.
The move immediately prompted a backlash from Russian President Vladimir Putin, who said it would damage U.S.