RIGA, Latvia — The European Union on Thursday urged six post-communist countries to move closer to the 28-nation bloc as a way to resist Russia's "bullying tactics" and build a brighter future for their citizens.

Speaking at the opening of a two-day summit in Riga, EU President Donald Tusk warned the former Soviet republics they had little to gain from falling back into Moscow's orbit instead of deepening their partnership with the West.

"The Eastern Partnership isn't a beauty contest between Russia and the EU," Tusk said. "But let me be frank, beauty does count. If Russia was a bit softer, more charming, more attractive, perhaps it would not have to compensate its shortcomings by destructive aggressive and bullying tactics against its neighbors."

German Chancellor Angela Merkel backed up Tusk's criticism of Moscow, saying that "the EU makes a crystal clear difference with Russia. We accept that the different Eastern Partnership nations can go their own way and we accept these different ways."

The EU's partnership program with Ukraine, Georgia, Moldova, Azerbaijan, Armenia and Belarus suffered a major setback 1 ½ years ago, when Ukraine's then-president Viktor Yanukovych withdrew from signing an association agreement and opted for closer links with Moscow and President Vladimir Putin.

After Yanukovych was ousted, Ukraine's new leadership turned back toward the EU but paid a heavy price: Russia annexed Crimea, large swaths of eastern territory bordering Russia are embroiled in conflict and the nation is in deep economic decline.

Meanwhile, Armenia and Belarus limited their relations with the EU by joining Russia's Eurasian Economic Union and Azerbaijan is showing little excitement about the EU partnership, sending its foreign minister to Riga instead of its president.

Ukraine, Georgia and Moldova are still seeking deeper integration, but many EU countries are reluctant to open the door for membership in the Western club.

The EU promised grants of 200 million euros ($223 million) over the next 10 years to promote small and medium-sized businesses in the three countries.

But Merkel on Thursday said the EU should not raise any false expectations in the talks with the eastern partners.

"The Eastern Partnership is not an instrument for (EU) enlargement but it is an instrument to get closer to the EU," Merkel said.

Eastern nations face many challenges to deepen ties with the EU, including improving justice systems and economic structures and fighting corruption.

Ukrainian President Petro Poroshenko assured that his country was ready to tackle corruption "and improve the investment climate."

The talks in Riga were expected to end Friday with a declaration that reaffirmed the Eastern Partnership but also touched on the conflict in Ukraine.

"Now we have the full evidence of the presence of the Russian army, the regular troops," Poroshenko said.

On the eve of the Riga summit, Russian Foreign Minister Sergey Lavrov told lawmakers that Moscow doesn't see "our neighbors' aspirations to strengthen ties with the European Union as a tragedy, but to make those processes develop positively they mustn't hurt the interests of the Russian Federation."

European leaders arriving in Riga stressed that the partnership was moving at different speeds due to the differing ambitions among the eastern countries.

Belarus and its authoritarian leader Alexander Lukashenko have also been kept at arm's length because of political and human rights complaints that earned the nation the moniker of the last dictatorship in Europe.

Icy relations have somewhat warmed recently and Belarus sent its highest delegation yet, led by its foreign minister, though it didn't include Lukashenko himself.

"It's important to stress that countries can make this progression individually, according to their own circumstances and demands," Swedish Prime Minister Stefan Lofven said. "I think that's one of the strengths of this partnership."