US ambassador to the UN Nikki Haley has fired back after a White House aide accused her of "momentary confusion" over new sanctions against Russia.
"With all due respect, I don't get confused," Ms Haley told Fox News television.
She was responding to comments by White House economic adviser Larry Kudlow.
On Sunday Ms Haley said the US was preparing new sanctions against Russian firms. But the White House later said no such action had yet been decided.
In her initial remarks, made on CBS television, Ms Haley said the fresh measures would target "any sort of companies that were dealing with equipment related to [Syrian President Bashar al-] Assad and chemical weapons use".
She said, the new sanctions would send a "strong message" to Russian leaders.
The statement angered President Donald Trump, The New York Times reported.The spat became public on Tuesday, when Mr Kudlow sought to clarify the administration's position on the sanctions.
He said Ms Haley was "doing a great job", adding: "There might have been some momentary confusion about that. I think the issue here is we have a set of sanctions and additional sanctions are under consideration but have not been determined."
Observers say the comment and the sharp response it drew from Ms Haley - denying being "confused", in an interview hours later - have further highlighted rifts within the administration.
Ms Haley is regarded as a major foreign policy figure in the administration, especially since the dismissal of Secretary of State Rex Tillerson last month.
Tensions between Russia and Western countries have risen since the US, the UK and France carried out strikes in Syria last week in response to an alleged Syrian chemical weapons attack.
Russia and Syria, its ally, insist that no chemical attack took place in the rebel-held town of Douma on 7 April.