The EU won't sacrifice its high food safety standards for better US auto market access in a transatlantic trade deal being negotiated, a German minister said Friday.

The comments by Agriculture Minister Christian Schmidt were the latest criticism of the thorny negotiations toward sealing a wide-ranging pact that would create a free-trade zone covering 850 million people.

Washington and Brussels want the Transatlantic Trade and Investment Partnership (TTIP) completed this year before US President Barack Obama leaves office, but it has faced mounting opposition on both sides of the Atlantic.

Schmidt told the German news weekly Der Spiegel that it was time for the United States to "at last make a move" if it wants the agreement.

"So far at least they have hardly made any serious concessions," the minister was quoted as saying in an early excerpt of the interview in Saturday's edition of Der Spiegel magazine.

US policymakers are wrong if it thought "they can lure us Germans with concessions in the automotive sector", he said.

"We won't sacrifice our high food safety standards in a barter trade for approval of European car blinkers," he said, in reference to industry standards on car parts.

"One has nothing to do with the other," he said. "There won't be any such horse-trading."

Environmental group Greenpeace on Monday released a trove of leaked documents about the closed-door negotiations, claiming that a deal would inflict a dangerous lack of standards on US and European consumers.

To some observers, the draft text suggested that the US side is trying to use the carrot of easing restrictions on auto imports from Europe for concessions on its agricultural exports, perhaps including genetically modified foods.

Germans are growing increasingly wary of the proposed pact, an opinion poll showed Thursday.

Some 70 percent of Germans polled by the dimap institute for broadcaster ARD said it would bring "mostly disadvantages", up from 55 percent in a similar poll in June 2014.

Chancellor Angela Merkel, meanwhile, this week reiterated her government's official position, saying that she would "do everything to conclude the negotiations", preferably by the end of 2016.

But German Economy Minister Sigmar Gabriel, a Social Democrat, warned last month that negotiations on the free trade deal "will fail" if the US refuses to make concessions.

"The Americans want to hold fast to their 'Buy American' idea. We can't accept that," he said.

France has also hit out at the pact, with President Francois Hollande saying this week that Paris would reject it "at this stage" because his country opposes "unregulated free trade".