The final round of talks between Chancellor Angela Merkels conservatives and the center-left Social Democrats got underway on Sunday to form a new coalition government. Merkel said it was unclear when her conservatives would be able to wrap up the talks and she expected the remaining negotiations to be tough. "Weve gathered here again today for the decisive round of negotiations. Its not yet possible to say how long it will last - We did good groundwork yesterday but there are still important issues that need to be resolved," she said before heading into negotiations. "Im going into talks with goodwill today, but I also expect that well face difficult negotiations in todays session," she added. The two camps aim to seal a deal by the end of Sunday to renew the "grand coalition" that has governed since 2013, although some politicians say they could run into Monday or Tuesday. The effort to put together a governing coalition is already post-World War II Germanys longest, and will not finish with these talks. A deal will require approval in a ballot of the Social Democrats members. Senior Social Democrat Manuela Schwesig said Sunday that "many questions remain open." She argued theres no point in pushing for a quick finish only to have party members ask a week later: "What nonsense did they negotiate?"