"I believe that we are open and confident enough to become the leading force in Europe. A force strong enough to fight poisonous populism and Euroscepticism. And to be strong enough to get at least one top position in the EU because liberalism must have key role in European politics," Šarec said.

"We don't want Europe to fall back into the past," Šarec said in his appeal ahead of the elections to the European Parliament in May next year in response to growing populism and xenophobia in Europe.

In his address the prime minister described Slovenia as an open and liberal country and as a country which believed in a strong and closely integrated EU.

As his LMŠ party was admitted to the ALDE today, he said he was proud to be one of the eight liberal prime ministers in the European Council.

In a press release, the Marjan Šarec List (LMŠ) said that the admission was an opportunity for the party to establish strong international links in a bid to increase its profile and influence in the EU.

The congress is also being attended by Slovenia's Foreign Minister Miro Cerar as the leader of the Modern Centre Party (SMC) and Roman Jakič from the Alenka Bratušek Party (SAB), whose leader serves as Slovenia's infrastructure minister.

In his speech, Cerar said that it was necessary to "reject all negative radicalism, all destroyers of the EU, be they on the left or on the right."

"Populists merely create fog to distract us from tackling real challenges such as poverty, sustainable development and global warming," he said.

Cerar urged liberal leaders to be "radical in our fight for normalcy, for human rights, for European democratic values and for principles that we have spent centuries fighting for."

The event was also addressed by Slovenia's member of the European Commission, Violeta Bulc, who said that the European elections would be an opportunity to take hope, faith, the power and respect for democracy into all corners of Europe.

The congress will confirm ALDE's platform for the Euro elections, where they hope to win sufficient vote to form the second strongest group in the European Parliament.

Guy Verhofstadt, the leader of the ALDE group in European Parliament, told the congress that the old bi-party political system led by socialists and conservatives would be eliminated in 2019.

ALDE leader Hans van Baalen announced that the liberals would enter the race as a team, which means they will not follow the system of Spitzenkandidaten.

On the sidelines of the congress, Šarec met his Danish counterpart Lars Lokke Rasmussen and Verhofstadt.

Verhofstadt also met Cerar with the Slovenian foreign minister tweeting that they agreed a joint appearance by Slovenian liberals in the Euro elections would create value added for Slovenia and Europe.