Lukšič, who took over from long-standing SD head Borut Pahor in June 2012, saw the SocDems lose one MEP on Sunday compared to the 2009 EU vote.

He was moreover defeated as the frontrunner on the SD slate by MEP Tanja Fajon, who won her second term thanks to 11,431 preference votes or 36.16% of the vote for the party. Lukšič was backed by 21.17% of the party's voters.

Lukšič explained for the press that the college of the party president had accepted his offer to resign today, while it also agreed with his proposal that Židan lead the SD until the election congress, which will be held as soon as possible after the general election. The choice of Židan remains to be confirmed by the SD's presidency on Wednesday.

The SD, which won the 2008 general election and was third in the 2011 election, has been losing ground to the Democrats (SDS) in recent public opinion polls and is moreover looking at a lot of competition from emerging new left-leaning parties.

While there has been much speculation about Židan, one of the most popular politicians in the country, taking over, the agriculture minister said on several occasions he was not interested in the job.

Židan said today that accepting to head the party until the congress had been a hard decision for him, but that the arguments in favour were so clear and support so strong that he "accepted this burden".

When asked whether he would stand for SD president at the congress, he said that "who will run and get elected will also be connected to the result of the [general] election".

Židan said the SD was looking forward to talks with like-minded left-leaning parties, expressing his conviction they will be able to win the election together.

Lukšič, a professor of political science at the Ljubljana Faculty of Social Sciences and education minister in the 2008-2011 Pahor government, is already the second party leader of the outgoing ruling coalition to resign in the wake of the EU election.

Gregor Virant stepped down as Citizens' List (DL) president immediately after the first official results showed the party only won 1.12% of the vote in Sunday's EU polls.