By Laurence Norman And Juris Ka a 

RIGA--Tensions among Europe's eastern neighbors broke to the surface on Friday, casting doubts about the European Union's flagship initiative to deepen economic and political ties with six former Soviet republics.

While EU leaders papered over divisions on whether to offer a path to eventual membership to their neighbors, it was tensions among the six--Ukraine, Moldova, Georgia, Armenia, Azerbaijan and Belarus--over Russia's actions in Ukraine and other regional issues that caused the biggest fights.

The disputes pointed to an increasingly obvious problem for the EU's Eastern Partnership initiative, launched in 2009 with the hope of setting the six countries onto a firmly western path. While Ukraine, Moldova and Georgia have incurred Russia's wrath by moving toward the EU, Belarus, Armenia and Azerbaijan have grown closer to the Kremlin.

Coming into this week's meeting in the Latvian capital, EU officials had warned there would be no big leaps forward in relations with its eastern partners in Riga. However they insisted the bloc's eastern outreach was still in good shape, citing trade and political deals with Ukraine, Moldova and Georgia in 2014 and fresh efforts to improve cooperation with Belarus, Azerbaijan and Armenia.

Yet by Friday morning, final agreement on a summit statement was being held up by Azerbaijan's unhappiness with wording on their conflict with Armenia over the disputed territory of Nagorno-Karabakh. Belarus and Armenia had also lodged repeated objections in recent days about language describing Russia's "acts against Ukraine" in 2014.

In the end, the summit close was delayed by over an hour as European Council President Donald Tusk made a last minute telephone call to Azeri President Ilham Aliyev, who had stayed away because of a deadly fire in Baku, to win his backing to what was agreed, diplomats said. Mr. Tusk confirmed the call.

The final text also had only EU leaders condemning the "illegal annexation" of Crimea by Russia, wording that ensured Belarus and Armenia didn't have to break with Moscow over last year's events.

In a final news conference, Mr. Tusk recognized the "difficulties" in agreeing a text, but said the EU had sent "a message of strong consistent and strong commitment" to the Eastern Partnership which was vital after "last year's intimidation, aggression and even war in this part of Europe." EU officials have said the bloc is adapting to regional developments through an increasingly "differentiated" approach which matches ties to the needs and interest level of partner countries.

Yet there has also been debate within the bloc over whether this could be the final Eastern Partnership summit--at least in its current form.

In an interview on Thursday evening, Latvian Foreign Minister Edgars Rinkevics said the Riga summit had avoided what some had feared: that the EU commitment to its neighbors was moving into reverse. However he acknowledged a "new phenomenon."

"Partners have probably on some issues more differences and to some extent, I would say that it was easier to forge a common stance within the EU this time than to try to find the mutually acceptable language...with these partners," he said.

For the Ukrainian, Georgian and Moldovan leaders, the summit statement provided at least some political cover.

It kept open a possible future door for EU membership if the countries pressed ahead with reforms, saying "summit participants acknowledge the European aspirations and European choice of the partners concerned."

EU leaders also signed off wording which looked favorably on Ukraine and Georgia's bid to win easier visa access to the bloc, a prize that Moldova won last year. EU leaders said "they look forward to the completion" of actions by the two countries that would allow them to win visa-free access to the EU. They pledged a review of progress before year-end.

The EU also formally signed off a EUR1.8 billion ($1.99 billion) balance-of-payments loan to Kiev, which it will disburse over the next year.

After the summit, Ukraine's President Petro Poroshenko told reporters he was satisfied with the results, saying the summit confirmed the EU's relationship with Ukraine was on a "high track."

The Ukrainian leader brushed off the objections of Belarus and Armenia to language condemning Russia's actions in Ukraine.

"On Crimea, when all the world has condemned the annexation of Crimea and one country doesn't see it, it's not a problem of the world, it's a problem of this particular country," he said.

Write to Laurence Norman at laurence.norman@wsj.com