A risky move

"We have better answers than the others," Steinmeier told a cheering crowd of around 2,500 at a party conference in Berlin on Sunday, April 19. "I want to govern as chancellor," he said.

Steinmeier underpinned his claim to topple conservative Chancellor Angela Merkel (CDU) by presenting his party's manifesto, which calls for increased taxes on the rich, while cutting them for those less well-off.

The Social Democrats (SPD) have pledged to boost the highest tax rate for people earning more than 125,000 euros ($163,000) to 47 percent from 45 percent, and to cut the lowest rate to 10 percent from 14 percent.

"Those with strong shoulders must now carry more weight in this crisis," Steinmeier said.

The proposed scheme also offers a 300-euro bonus for taxpayers who do not file a tax return to claim small rebates, a move that will cut red tape, according to the Social Democrats.

Who's to blame?

Steinmeier also directed scathing criticism at those he said were responsible for the global financial crisis.

"Something is smoldering in our country," he said. "Anger and indignation are rife. The people's sense of justice has been violated.”

The foreign minister blamed the casino-style action on the stock markets for the current crisis, adding that executives' global hunt for maximal return had changed the foundations of society.

Steinmeier also emphasized his party's aim to defend the rights of employees and their jobs, including a realistic minimum wage with a benchmark of 7.50 euros.

He added that struggling German carmaker Opel, which employs some 26,000 people in Germany alone, had to be saved at all costs.

SPD shifts left amid economic crisis

With unemployment on the rise, the handling of the economic crisis is set to be a major battleground in the campaign and Steinmeier's comments as well as his party's tax plans are aimed at boosting the party's flagging popularity.

Judging by the reaction of Germany's largest parties, however, the SPD's tax plans could reduce coalition options or at least seriously impede coalition negotiations following September's election.

The leader of the pro-business Free Democrats (FDP), Germany's biggest opposition party, said the SPD plan effectively ruled out an alliance with his party.

"On this basis, there can be no collaboration," said Guido Westerwelle. Raising taxes might go down well with the Greens and the Left party, he said, "but not with me."

Political flip-flopping?

Even the Greens, the SPD's preferred coalition partner, were critical of the manifesto.

"What the SPD is proposing today is the opposite of what they did during four years in the grand coalition. So we have to ask them: 'Are you really serious?'," the Greens said in a statement.

Angela Merkel's conservatives -- the SPD's senior partner in Germany's uneasy grand-coalition government -- also attacked Steinmeier's proposals.

The general secretary of Merkel's CDU party, Ronald Pofalla, dubbed Steinmeier "Wobbly Walter" and said that the SPD "shift to the left is now a done deal."

Pofalla accused the SPD of not only raising existing taxes but also of introducing new taxes. "We want to cut taxes," he pledged.

The grand coalition of SPD and CDU has been shaky ever since its inception following the election stalemate four years ago. Both parties are hoping to govern with a more agreeable and smaller coalition partner after the September poll.