"The use of a highly lethal nerve agent against UK citizens on UK soil is an outrage," said press secretary Sarah Sanders. "The attack was reckless, indiscriminate and irresponsible."
Sanders stopped short of pointing the finger of blame at Moscow, as British Prime Minister Theresa May did earlier in parliament.
When asked whether Russia was to blame, Sanders demurred: "We stand by our ally and fully support them."
The United States and Britain have a long-standing intelligence-sharing agreement.
A British government spokesperson told AFP: "There have been conversations between senior US and UK officials. There will be more contact over the coming days."
May said Monday that the nerve agent was military-grade and developed by Russia.
Moscow has repeatedly denied any involvement, and earlier warned London that in attributing blame, it was playing a "dangerous game" that risked harming bilateral ties.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)