Germany's 65-year-old former finance minister won 93.45 percent support from the Social Democrats (SPD), officially naming him as the party's man to challenge Angela Merkel in the next federal election, likely to take place in September. Earlier in the week, Merkel won a similar Christian Democrat vote by an even clearer margin, claiming over 98 percent of her party's support.

Prior to his election, Steinbrück - who had already been announced as candidate in waiting - delivered a combative 105-minute speech to the party at its conference in Hanover.

"I am running for the office of chancellor of the Federal Republic of Germany," Steinbrück said, telling his allies "we owe it to this country to once again provide a Social Democratic chancellor."

Watch video 01:06 Social Democrats place hopes in Steinbrück

He called the ruling Christian Democrats - who are comfortably the most popular single German party in opinion polls - a "power machine."

"But retaining power is not the central target in politics," Steinbrück said, saying that Chancellor Merkel would too often speak in "popcorn sentences" - phrases that could be interpreted in many ways and offered little concrete substance.

"With Frau Merkel, many things remain vague - and that's not without its dangers," Steinbrück said.

A Green or a Grand coalition?

Judging by public broadcaster ARD's most recent opinion polls, a change in German government is currently likely at the next elections - but what shape that might take is unclear. Merkel's junior coalition partners are in freefall, meaning that the current alliance with the pro-business Free Democrats looks unlikely to survive.

Some say the most likely constellation would be a so-called "grand coalition;" an alliance between the Christian Democrats and the Social Democrats. Steinbrück served as finance minister in such a government, but said he did not want to see it repeated.

Calling for "a full change in government," not half measures, Steinbrück told delegates "the answer as to how this could work is quite obvious: red-green."

The SPD's party color is red, and its closest ally in opposition currently is the ecologist Green Party. Combined, the two parties are six percent shy of the 50-percent level of support they would need to form a government. Even though the SPD trails the Christian Democrats by nine percent, the combined pair are polling one-percent more strongly than the current coalition government.

With neither the natural left or right coalitions currently on course to win a majority, Steinbrück also urged his Social Democrats to stay unified during the election campaign to improve their standings.

"If we march side-by-side, then we will manage it," he told the delegates.

msh/pfd (AFP, dpa, Reuters)