US Embassy in Kiev. Photo: govexec.com

Responding to a question about leaked classified documents from the US Department of Defense suggesting that US special forces are operating inside Ukraine, Kirby said:

"I won't talk to the specifics of numbers and that kind of thing. But to get to your exact question, there is a small US military presence at the embassy in conjunction with the Defense Attachés office to help us work on accountability of the material that is going in and out of Ukraine."

However, Kirby added that those troops "are not fighting on the battlefield."  There has been no change to the President's mandate that there will not be American troops in Ukraine fighting, he said.

The Guardian earlier reported it had access to two classified Pentagon documents drafted in late February and early March, which suggested that, as of March 1, about 97 NATO special forces personnel were active in Ukraine, including 50 Britons, 14 Americans and 15 French nationals.

The Pentagon and the US Department of Justice have launched an investigation into the documents leak.