Speaking to reporters in Washington, U.S. Assistant Secretary of State for Democracy, Human Rights, and Labor Michael Posner announced that U.S. Secretary of State Hillary Clinton would participate in the meeting.
He said Belarus will be high on the agenda.
"The environment [in Belarus] is terrible," Posner said. "The government has cracked down not only on the political opposition but [on] civil society and a range of others. So we're deeply concerned about it, we're going to continue to press, we can't do it by ourselves and we need out European partners. We will have this very much on the agenda in Lithuania."
Posner also said that the United States and Russia "don't see eye-to-eye" on the crackdown under Belarusian President Alyasandr Lukashenka, meaning the West must ramp up its own pressure on Minsk.
The Vilnius gathering runs from June 28-July 1 and will also host a "tech camp" to train civil-society activists, mostly from Belarus.
Moldova and emerging democracies in North Africa will also feature in the meeting's discussions.
Founded in 2000, the Community of Democracies brings together government officials and civil society leaders with the goal of strengthening democratic values around the world.