Biden held separate meetings with Georgian President Georgy Margvelashvili and his Moldovan counterpart Nicolae Timofti on the sidelines of Western-backed tycoon Petro Poroshenko's inauguration as Ukraine's head of state.
The White House said Biden pledged $5.0 million (3.7 million euros) in additional assistance to Georgia pending Congressional approval.
It noted that Washington was now providing the Caucasus nation of five million people approximately $65 million in assistance this year.
Much of that aid is aimed at helping Georgia deal with the social consequences of its loss of two rebel territories following a brief 2008 war with Russia.
Biden also pledged $8.0 million in assistance to Moldova -- Europe's poorest nation whose eastern Transdniestr region is seeking to merge with Russia -- pending Congressional approval to help it "advance its European aspirations".
Both countries are expected to brush aside Russian pressure and sign historic EU trade and political association agreements at a summit in Brussels next month.
Poroshenko was sworn into office following snap elections that were called after the February ouster in Kiev of a Moscow-backed president who had rejected an identical EU pact.