Chancellor Angela Merkel said on Sunday she was optimistic her conservatives and the Social Democrats (SPD) could agree to join forces as they embarked on five days of talks about reviving the 'grand coalition' that has governed Germany since 2013.
Persuading the SPD to team up with her is Merkel's best bet of forming a stable government in Europe's largest economy and extending her 12 years in office, after her attempt to form an alliance with two smaller parties failed last year.
Arriving at SPD headquarters for talks more than three months after a national election, Merkel said the parties had a lot of work to get through in the coming days but intended to tackle it quickly, adding: "I think it can succeed."
The SPD, which had said it would go into opposition after its worst election showing since 1933, reconsidered when Germany's president intervened.
But the centre-left party, among whose membership opposition to a 'grand coalition' re-run remains strong, has been playing hard-to-get.
A group called "NoGroKo", meaning "no grand coalition", has formed within its ranks to campaign against working with Merkel again, saying that would cost the SPD votes and make the far-right Alternative for Germany (AfD) the leading opposition party.
SPD leader Martin Schulz said that, while the outcome of the talks was unclear, his party would enter them constructively.
"We won't draw any red lines - rather we want to push through as much red politics as possible in Germany," Schulz said, referring to the party's colour.
Schulz said five days should suffice to find out whether the parties had enough common ground to launch full-blown coalition talks. The SPD leadership is due to recommend on Friday whether or not to start talks, and it is then up to an SPD party congress on Jan. 21 to make a decision.