The initiative will see the EU treat the ex-Soviet states as a regional bloc
The European Union has launched a plan to forge close political and economic ties with six former Soviet republics in exchange for democratic reforms.
The Eastern Partnership Initiative agreed in Prague is intended to bolster stability in the region, but without the prospect of eventual EU membership.
The EU will invest 600m euros (£535m; $804m) in the project up to 2013.
Russia has accused the EU of trying to carve out a new sphere of influence in what Moscow sees as its own backyard.
The Russian Foreign Minister, Sergey Lavrov, has repeatedly warned against the creation of new dividing lines in Europe
The EU is following up with another summit on Friday aimed at opening a "southern corridor" for energy supplies, mainly through a long-planned pipeline to bring gas from Central Asia to Central Europe that would bypass Russia.
The Eastern Partnership Initiative was launched in the Czech capital late on Thursday after being signed by representatives of the EU, Armenia, Azerbaijan, Belarus, Georgia, Moldova and Ukraine.
The main goal of the partnership was to "accelerate political association and further economic integration" between the EU and the former Soviet nations, the participants said in a joint statement.
The new initiative will see the EU treat the former Soviet states as a regional bloc and establish free-trade areas with them, as well as offering millions of euros of economic aid, technical expertise and security consultations.
In return, the partnership obliges the six countries to commit to democracy, the rule of law and sound human rights policies.
"The Eastern Partnership will seek to support political and socio-economic reforms of the partner countries, facilitating approximation toward the European Union," the statement said.
Demands for visa-free travel for citizens of the six countries were blocked, however, while the declaration was amended to call them "East European" rather than "European" so as not to encourage applications for EU membership.
The EU leaders were also keen to stress that the initiative was not directed against Russia, saying it could join in certain future projects if it wanted.
"As we said during the summit, this is against nobody. When we increase prosperity, when we increase stability, we're increasing it not only for us but for all the others as well," said European Commission President Jose Manuel Barroso.
The BBC's Oana Lungescu in Prague says that for Ukraine and Georgia, which see their future in the EU, the summit offered a roadmap to get there.
"This is a step closer to a family," said Georgian President Mikhail Saakashvili. "There is no way back."
In other developments, diplomats said the presidents of Armenia and Azerbaijan, who met separately on the margins, had made serious progress on resolving their long-standing dispute over the region of Nagorno-Karabakh, our correspondent says.