BERLIN — Germany's Social Democrats (SPD) suffered a humbling blow on Sunday, failing to win the most votes in the state of Bremen for the first time in 73 years, but their leader vowed to stay in government with Angela Merkel's conservatives.

The humiliating result predicted in an exit poll will intensify pressure on SPD leader Andrea Nahles to stand down and break with the federal coalition at the end of the year. However she received applause after telling members at SPD headquarters to keep their chins up despite the disappointing results.

"Now it is important that we continue to work in the coalition to ensure a socially just government policy, including a basic pension," said Nahles, adding the party was renewing its program and there was no point in giving up half way through.

The Bremen poll came as both the SPD and Merkel's conservative bloc suffered losses in European elections, bleeding support to the Greens.

In the eastern state of Brandenburg, the far right Alternative for Germany (AfD) was the biggest party in the European elections, winning 21.2 percent of the vote. Brandenburg is one of three eastern states holding elections in September and October.

Bremen is Germany's smallest state and the SPD may still end up sharing power in a three-way leftist coalition, but second place represents a major setback in its northern bastion.

Merkel's Christian Democrats (CDU) came first in Bremen with 25.5 percent, an exit poll for ARD television showed. The center-left SPD won 24.5 percent of the vote, down from 32.8 percent in 2015. The resurgent Greens are probable kingmakers by virtue of an 18 percent share, according to the exit poll.

Final results are expected tonight or early on Monday.

Many among the SPD's rank and file are fed up with serving as Merkel's allies, a role the party has taken in 10 of the past 14 years, leaving the chancellor to steal the limelight, especially on the international stage.

The SPD reluctantly re-entered a Merkel-led coalition last year after slumping to its weakest level of support since 1933 in the 2017 federal election.

The party is due to review the coalition by the end of the year, and pressure from members could grow to leave and reinvigorate its leftist roots in opposition. This could force a snap federal election or a search for a different coalition.

Both options are unappealing for the SPD and conservatives alike, and could hasten Merkel's exit as chancellor, a subject of growing speculation since she handed over leadership of the CDU to protege Annegret Kramp-Karrenbauer last year.

Senior party members rallied round Nahles while agreeing that renewal was needed.

"This result cannot go without consequences," said SPD General Secretary Lars Klingbeil, adding, however, that this was not the time to start a debate about who has what job.

German weekly Bild am Sonntag reported that former SPD leader Martin Schulz wants to replace Nahles as head of the parliamentary party. An SPD spokeswoman said Nahles and Schulz were in regular discussions but the talks were confidential.

Several commentators warned of turbulent times ahead as the SPD tries to rediscover its identity.

"The loss of its pivotal role in Bremen is another manifestation of the SPD’s seemingly endless decline," said Carsten Nickel, managing director at consultancy Teneo. "In Berlin, the calls for quitting Merkel’s grand coalition will only get louder."

Many analysts argue that SPD lawmakers will want to avoid an early election to keep their job, but others have warned that the chances of a fresh poll are rising.

"No longer excluded, there will be snap elections in Germany still this year. SPD could leave government," tweeted Henrik Enderlein, president of the Hertie School of Governance. — Reuters