Georgia's President Giorgi Margvelashvili and Ukraine's Petro Poroshenko will attend the Atlantic alliance's summit in Warsaw on Friday, but as partners not as full members.
With large chunks of both countries already occupied by Russian forces, there is no prospect of either former Soviet republic joining NATO's mutual defence pact soon.
Washington, however, is keen not to cede any more ground to President Vladimir Putin's newly assertive Russia, and Kerry's visit to Kiev and Tbilisi is more than a symbol.
"These are important members of the alliance, partners whose security means a lot to the United States," she said.
Also Read
"Their security interests and Euro-Atlantic aspirations - their aspirations to get closer to the European Union and NATO - matter to us," she added.
Asked how the Kremlin might see such a visit ahead of the NATO summit, she smiled and said: "Russia can take whatever message it likes from this."
During this week's NATO summit, billed as the most important in a quarter century, member states are expected to re-endorse Georgia's eventual membership.
"We do see their future with NATO, but there's more work to be done," she admitted.
David Bakradze, Georgia's Minister for European and Euro- Atlantic Integration, told AFP that the visit will take ties with the US "to a qualitatively new level" and help to bolster Georgian security and economic and democratic development.
Since a brief war in 2008, Russian troops have tightened their grip over the breakaway Georgian regions of Abkhazia and South Ossetia, putting them 20 minutes drive from the vulnerable capital.
Putin's army has also occupied Ukraine's Crimea region, and he has backed pro-Russian separatists in the east of the country, creating another headache for NATO planners.