BERLIN - Germany's Social Democrats (SPD) on Sunday formally endorsed former European Parliament President Martin Schulz as their leader and challenger to Chancellor Angela Merkel in what is set to be a tightly contested national election in September. 

The SPD has undergone a revival since nominating Schulz in late January, gaining around 10 points in opinion polls and signing up thousands of new members as the 61-year-old focuses his campaign on social justice.

"The SPD is back! We're back!" Schulz told around 600 delegates at a party meeting in Berlin shortly before he was chosen as SPD leader in a vote in which all 605 of the valid votes gave him a 'yes'.

Delegates signalled with their hands they also wanted him to run for the SPD in the Sept. 24 election.

He also reiterated his calls for free education, more investment such as in nursing care and schools.

as well as qualification programmes for the unemployed in a speech that earned him a standing ovation. It is necessary to close the "intolerable pay gap" so men and women in both eastern and western Germany get the same amount of pay for doing the same work, Schulz said.