BERLIN: German Chancellor Angela Merkel's conservatives and the Social Democrats (SPD) negotiated through the night into Wednesday in a marathon final push to try to nail down a new coalition agreement. Negotiators from the two blocs remained locked in talks just before dawn at the headquarters of Merkel's Christian Democrats, where they began meeting at 10 am on Tuesday. Merkel's failure to cobble together a government more than four months after a national election has raised concerns among investors and partner countries at a time when Europe is facing multiple challenges - including the need for euro zone reform and Britain's departure from the European Union. The SPD suffered its worst result in last September's national election since Germany became a federal republic in 1949 and initially vowed to rebuild in opposition. However, party leader Martin Schulz changed course and opened negotiations with Merkel after she failed to clinch a coalition deal with two smaller parties in November. Vowing to negotiate until the conservatives 'squeal', the SPD has been trying to extract concessions on healthcare and employment policy that could win over sceptics among its 464,000 members, who get the final say on whether to go ahead with the coalition. Sources involved in the negotiations said the conservative bloc had reopened topics that had previously been agreed. Both Merkel's conservative bloc and the SPD are under pressure not to concede too much in the negotiations or see their support ebb further. An Insa poll on Monday showed support for the SPD dropping to 17 percent, below its election result of 20.5 percent. The conservatives slipped to 30.5 percent, suggesting there would be no majority for a grand coalition if an election were held now.