The United States is concerned that a Russian-directed counteroffensive is "likely underway" in Donetsk and Luhansk in eastern Ukraine, State Department spokeswoman Jen Psaki said Wednesday, citing Russian troops and equipment pushing into Ukraine, shelling in residential towns near the border and heavy fighting near the airport in Donetsk.

"These incursion - incursions - indicate a Russian-directed counteroffensive is likely underway in Donetsk and Luhansk. Clearly, that is of deep concern to us," she said.

One potential consequence of Russia's advance is its ability to create a land bridge between eastern Ukraine and the region of Crimea, which Russia officially claimed as its own in March.

"It's hard for us to ascribe what the motivation is, but certainly we're closely watching this incursion and any steps [Russia] is taking in southeastern Ukraine, whether it's next to Crimea or not," she said.

Psaki said the U.S. is also troubled by the fact that Russian soldiers have been found 30 miles inside Ukraine, and, according to videos released by the Ukrainian government, were not told where they were going by their commanders.

"Russia is sending its young men into Ukraine, but [is] not telling them where they're going or telling their parents what they're doing," she said.

News of Russian troops and equipment entering Ukraine is only the latest development in fighting that sprouted from protests over the previous, pro-Russian government that was later ousted. Pro-Russian separatists have sought to take over parts of eastern Ukraine, but in recent weeks have been pushed back by the Ukrainian military.

Russia's actions over the past 24 hours could be an indication it's trying to shift the balance toward the rebels in the east against the central Ukrainian government.

Despite voicing these concerns, Psaki did not announce any plans by the United States to further punish Russia on top of economic sanctions already imposed since Russia began its move on eastern Ukraine.

She said President Obama would likely discuss Russia's actions next week at a NATO leaders' summit in Wales.