The Pentagon says Russia continues to send in troops along Ukraine's eastern border for what it says are exercises, but so far the U.S. has not seen evidence that those exercises have taken place.

Pentagon Press Secretary Rear Admiral John Kirby told reporters today that the U.S. remains concerned about the growing troop presence along the eastern Ukrainian border and it's unclear what their intent is.

He would not say how many troops have gathered there beyond saying, "thousands … there's no question about that."

Several U.S. officials have told ABC News that Russia has gathered about 30,000 troops in various locations along Ukraine's eastern border.

Kirby said Russia continues to boost its forces and that we "remain concerned about that. We're monitoring it closely."

Last week, Russian Defense Minister Sergei Shoigu assured Defense Secretary Chuck Hagel that the troops are there for springtime military exercises and have no intention of crossing into Ukraine.

Kirby echoed Hagel comments on Wednesday that Russia needs to live up to its word even though "we've seen no specific indications that these exercises are taking place."

He deferred to the Russian Defense Ministry as to "what they're going to do with them." He also explained that though there have been no indications of exercises it does not mean that they won't occur.

"They have amassed troops along that border. They have them in quite a number and in a composition that provides lots of capability," said Kirby. "They made it clear that their intent was to do exercises and not to cross the border. Our expectation is they're going to live up to that word."

Regardless of intent, Kirby said that Russian military exercises in that region do nothing "to de-escalate the tension in Ukraine."

He added, "It does nothing to improve the stability in that part of the world. And so in that regard, you know, it's certainly a matter of deep concern to us."

He would not speculate if the size of the Russian military force indicated they would be able to sweep into eastern Ukraine with no notice.

Ultimately, Kirby said that there is a limit to the amount of knowledge that the U.S. about what's happening on the Russian side of the border.

"I think there is this expectation that we know exactly - not only how many, but what their names are and what units they're attached to, and we simply - you know, you're not going to have perfect knowledge in that case," said Kirby.

Kirby said the U.S. is focused on non-lethal assistance to Ukraine - so far the only concrete decision has been to provide 25,000 Meals Ready to Eat for Ukraine's military. He said those MRE's would arrive by land this weekend. He would not confirm that the U.S. has provided intelligence to Ukraine about Russia's military moves along its border.

On Wednesday, British Defense Minister Philip Hammond said Russian President Vladimir Putin was in control of the Russian agenda for Ukraine and that Shoigu might not be part of the inner circle involved in the decision-making.

Asked if Hagel shared Hammond's assessment, Kirby said, "I don't think there's any gap between Minister Hammond's concerns and Secretary Hagel's in that regard."