"We are reassuring and reinforcing the sovereignty of countries that are on the frontlines of Russian aggression," said a senior defense official.

Georgia and Ukraine have areas occupied by Russia. Russia invaded Georgia in 2008 and occupied South Ossetia and Abkhazia — roughly 20 percent of the nation. Ukraine is in conflict with Russia, and Russian forces have killed around 14,000 Ukrainians in and around the Donbass region in Eastern Ukraine since 2014. Russia also illegally annexed Crimea.

Austin will stress in both Georgia and Ukraine that there is an open door to NATO and encourage the nations to make the changes necessary for them to qualify for membership in the defensive alliance.

Austin is also going to recognize the nations for their support. "In terms of sacrifices, it is important to note that Georgia … was the top, per capita contributor to the Resolute Support Mission in Afghanistan, and suffered many losses from that mission," the official said.

All three countries border the Black Sea, and Austin will speak to their leaders about Black Sea security and seek to strengthen cooperation among these nations.