'Putin will go as far as the West allows him to'

"If we allow Russia to hold a referendum under the barrel of Kalashnikovs on the annexation of Crimea, we will lose stability throughout the whole world," she said.

Still in a frail state after more than two years in prison, Tymoshenko confirmed reports she will fly to Germany for medical treatment.

In a wheelchair, she was accompanied on stage by her daughter, Eugenia, who campaigned tirelessly for her mother's release. They were both welcomed with standing ovations and flowers.

The EPP has consistently pleaded for Tymoshenko's release, with the party's late chief, Hans Martens, a strong supporter of the Ukrainian politician.

But other EPP leaders, notably Germany's Angela Merkel, were concerned about giving Tymoshenko too much of a platform. The former prime minister is a polarising figure in Ukraine, after controversial gas deals with Russia's Vladimir Putin.

EUobserver has learned that Merkel insisted that other opposition figures be invited to the EPP congress. Vitali Klitschko and Arsenyi Yatsenuk were added as speakers, although the latter was unable to make it to Dublin.

Klitschko and Tymoshenko appeared together for press photos but chose to hold their press conferences separately.

Of the two, Klitschko seemed more inclined to co-operate.

"I have been working together with Tymoshenko's party against the regime and I hope to do so in the future," Klitschko said.

He said that as a former boxer he "knows better than anyone: no fight, no win".

Ukraine will "defend itself", he said, but not seek war with Russia.

As for Tymoshenko, she mentioned no other opposition party and defended her relations with Putin during her time as prime minister, but said she had no contact with him since being in jail.

"I had to work with Putin when I was prime minister. I tried to build a relationship with Russia so Ukraine is not just a 'little brother'," she said during her press conference.

As for future co-operation with Russia, Tymoshenko doubted there can be direct bilateral relations as long as they are "unequal" and Russia is in violation of international agreements regarding Ukraine's territorial integrity.

"If Russia is allowed to annex Crimea, the whole of Europe will be on the losers' side. I will not accept a compromise at Ukraine's expense, and that includes its territorial integrity," she said.

According to Russian media reports, Tymoshenko allegedly struck a deal with Putin so he can keep Crimea, while she gets his endorsement for becoming prime minister after the May elections.

Tymoshenko responded to this by saying: "Don't watch Russian TV, don't read Russian press, it's full of anti-Ukrainian propaganda."

On recent remarks by Estonian foreign minister Urmas Paet (made in a leaked telephone call) that there was a "stronger understanding" among Maidan protesters that someone in the current interim government, and not ousted President Yanukovych, had hired snipers to shoot at civilians, Tymoshenko said she "fully supports an independent inquiry".

"Experts are already on the ground," she added.