When Sanders was asked about this development and whether there would be any repercussions, the press secretary called the attack an "outrage", but did not explicitly blame Russian Federation.
"The attack was reckless, indiscriminate, and irresponsible".
"We stand by our closest ally and the special relationship that we have".
Asked if she was suggesting this meant Russian Federation was not responsible, she replied: "Right now, we are standing with our United Kingdom ally. I think they're still working through even some of the details of that", Sanders said.
The Trump administration has faced criticism for its muted criticisms of Russia and Russian President Vladimir Putin after the US intelligence community determined Russia sought to interfere in the 2016 presidential election.
Mr Skripal and his daughter are still being treated in hospital after falling ill in Salisbury.
"We will not tolerate such a brazen attempt to murder innocent civilians on our soil", she said.
May said Russia's ambassador in London had been summoned to the Foreign Office to explain whether the attack was "a direct action by the Russian state" or the result of the Russian Government "losing control" of its stock of nerve agents.