State Department spokeswoman Heather Nauert said Russia was like a beast with "long arms" and "lots of tentacles."
The tests come as Russian President Vladimir Putin revealed new nuclear missiles and Moscow's relationship with the West took another major blow.
At least 20 countries expelled 139 suspected Russian spies in solidarity with the United Kingdom.
At least 20 countries have kicked out more than 130 Russian diplomats, believed to be covert intelligence officers.
The U.S., Germany, France, other EU countries and Ukraine have all announced they are expelling Russian diplomats.
Four countries bordering Russia reportedly called in Moscow's top diplomats on their territory as the EU decided its response to spy poisoning scandal.
Sergei Skripal and his daughter are being kept heavily sedated and are still unable to communicate two weeks after they were poisoned.
The back-and-forth blame has continued between British and Russian officials since the March 4 incident.
The foreign ministers of both countries took aim at each other.
Russian Foreign Minister Sergey Lavrov says Moscow will "soon" expel British diplomats in a tit-for-tat response.
An ex-spy, his daughter and a police officer are seriously ill. So what exactly is Novichok?
Asked three times about Russia's involvement, White House press secretary Sarah Sanders repeatedly stated, "We are standing with our ally."
The Kremlin may have ordered a hit on an ex-Russian spy in the U.K. But some point to a scarier prospect—that Moscow's death squads did it on their own.
Investigators did not identify which nerve agent was used on the pair, but the best-known nerve agents are sarin and VX.
Convicted Russian spy Sergei Skripal's "substance exposure" is drawing comparisons to the 2006 death of Russian intelligence agent Alexander Litvinenko's acute radiation poisoning.