(AP Photo/Pavel Golovkin)
(AP Photo/Pavel Golovkin)

There's growing concern among U.S. observers about the number of Russian troops amassing on Ukraine's border.

FOX News Radio's Steve Taylor reports from Washington DC:

U.S. intelligence says Russia is behaving the way it did before it entered Crimea. Russian leaders talk about supposed "brutality" against Russian-speaking Ukrainians. And, Russian troops are now deployed along the border with eastern Ukraine. Pentagon spokesman John Kirby:

Kirby: "It's certainly, a matter of deep concern to us".

Moscow says the troops are on military exercises. But Defense officials estimate there are 30,000 of them, which suggests more than training, and they're not going back to their bases.

In Washington, Steve Taylor, Fox News Radio.