BERLIN (Reuters) - Germany’s Social Democrat (SPD) environment minister said on Thursday she expects party members to support a new coalition government with Chancellor Angela Merkel’s conservatives by a margin of 60 percent.

Social Democratic Party (SPD) flags are pictured during the traditional Ash Wednesday meeting in Vilshofen, Germany February 14, 2018. REUTERS/Michaela Rehle

The SPD’s 464,000 members are voting in a postal ballot on whether to endorse their party leadership’s decision to renew for another four years the ‘grand coalition’ that took office in 2013. The result of the postal ballot is due on Sunday.

“I expect it to turn out positively,” Environment Minister Barbara Hendricks told a news conference in Berlin. “I expect around 60 percent (approval).”

An opinion poll on Thursday showed rising support for both blocs, with Merkel’s conservatives gaining one point to 34 percent and the SPD rising 2 points to 18 percent.

The conservative bloc, comprising Merkel’s Christian Democratic Union (CDU) and the Bavarian Christian Social Union (CSU), embarked on coalition talks with the SPD after negotiations with two smaller parties failed last November.

Senior officials from the CDU, CSU and SPD met in the chancellery on Thursday to iron out outstanding issues on the formation of a coalition government, party sources said.

The SPD members’ ballot runs until Friday.

A poll released on Wednesday showed a narrow majority - 56 percent - of SPD voters in favor of a re-run of the grand coalition. However, the poll surveyed a far broader group than the party members taking part in the decisive ballot.

The CDU approved the coalition deal on Monday, bringing closer a fourth term for Merkel as well as an end to political limbo in Europe’s preeminent power. The chancellor said she hoped the SPD would also back the deal.

CSU leader Horst Seehofer said on Wednesday Germany should hold a new election if SPD members vote against a coalition with her conservative bloc.

Merkel has been more guarded on the issue of a minority government since November, when she said after the breakdown of coalition talks with the business-friendly Free Democrats and environmentalist Greens that she would prefer a new election to leading one.