"Obviously, we cannot discuss the specifics of this, but you can probably draw your own conclusions," the official told journalists.
Another senior administration official said during the briefing that the expelled "worked under diplomatic cover and were undeclared Russian intelligence officers."
"What we are going to do is to continue to put pressure on Russian intelligence officers around the world and working with our partners because the action we took was in our security interest," the official said during a press briefing.
The United States is "very satisfied" that countries around the world chose to expel Russian diplomats in response to the attack on ex-Russian spy Sergei Skripal in Britain, official told reporters.
"Yes, we are very satisfied with the scope of the response around the world. I think today the total number (of countries that expelled diplomats) is over 30, including the US and NATO," the official said.
He added that the the total numbers of expelled diplomats from different countries depended on each country's level of diplomatic representation in Moscow.
"The small country has smaller representation. So, their willingness to expel one person is significant because they are risking their own missions in Moscow," the official said.
On Monday, the US government announced the expulsion of 60 Russian diplomats and the closure of the Russian Consulate General in Seattle. Washington said the move comes in response to the attempted murder of former spy Sergei Skripal and his daughter Yulia with a nerve agent in Salisbury, England.
Russia has repeatedly denied any connection to the Skripal case and has asked for a joint investigation in the matter, but Moscow’s request has been rejected. Russia has also said no evidence has been offered to back any of the Skripal case claims against it.