BERLIN — Chancellor Angela Merkel’s conservatives and their prospective center-left partners in government faced criticism Tuesday over their reported willingness to push back Germany’s target for reducing carbon dioxide emissions by 2020.

Merkel’s Union bloc and the center-left Social Democrats are holding preliminary talks this week on extending their coalition of the past four years. Conservative negotiator Armin Laschet told a business group Monday they had wrapped up talks on energy policy, but gave no details.

German news agency dpa reported that the agreement involves officially giving up the country’s target of a 40 percent cut in carbon dioxide emissions by 2020 compared with 1990, regarded by many as unachievable, but taking measures to close the gap as far as possible.

The Redaktionsnetzwerk Deutschland newspaper group reported that the new aim would be to reach the target “at the beginning of the 2020s.”

Merkel, who pledged before September’s election to stick to the 2020 target, has been dubbed the “Climate Chancellor” for her ambitious aims for renewable energy. Germany still gets about 40 percent of its electricity from coal-fired plants.

The country plans to abandon nuclear energy by 2022, but Merkel has resisted calls to set a deadline for ending the use of coal — including the crumbly brown variety known as lignite that still is mined in Germany.

Laschet, the governor of North Rhine-Westphalia state — a region known for lignite mining — stressed that Germany wants to comply with the 2020 targets set under the international Paris climate agreement. He argued it can’t do so by “suddenly saying we are getting out of an energy source, lignite, without knowing what consequences that has for jobs, but also for energy prices.”

A prominent member of Germany’s opposition Greens — who were involved in Merkel’s failed previous effort to form a government with two smaller parties — said the direction of the potential “grand coalition” of Germany’s biggest parties was worrying.

“Who is going to fight for an exit from coal or a real reduction of CO2 emissions in the ‘grand coalition’?” asked Robert Habeck, who is running for the Green party’s leadership. “There is no one I can see.”

Negotiators in the preliminary governing talks said Tuesday that any agreement on specific issues depends on them reaching an overall deal.

“Nothing is fixed,” said Andreas Scheuer, the general secretary of the Christian Social Union, the Bavaria-only branch of Merkel’s Union bloc.

Laschet’s comments nonetheless caused irritation, since the parties had agreed not to discuss details publicly before they decide whether they have enough common ground to move on to formal coalition negotiations.

Scheuer said negotiators were closing in on the big issue of the next government’s financial priorities.

Moving on to formal talks would require the approval of a Social Democrat congress. The party’s leadership, who initially said the Social Democrats would go into opposition following a disastrous election showing in September, will have to overcome strong reservations among members.