He told representatives of EU delegations that the likely signing of the Association Agreement with Ukraine at the summit in the Lithuanian capital was a test to the entire Eastern Partnership program.
"The Eastern Partnership summit that we will hold in Vilnius in November could be highly significant," Van Rompuy said in his speech.
"The signing of the partnership agreement with Ukraine, a real test for the Eastern Partnership as a whole, will be on the table. It requires further important steps from Ukraine. It's an historic opportunity for them, and we will remain in contact with (Ukrainian) President (Viktor) Yanukovych on this issue," he added.
The EU Eastern Partnership summit will take place in Vilnius in the end of November. The Eastern Partnership involves Armenia, Azerbaijan, Belarus, Georgia, Moldova, and Ukraine.
