Germany's economy minister lashed out at Chancellor Angela Merkel for her "wrong" stance on a huge EU-US free trade pact in an interview to be published Monday, signalling a deepening rift within the government over the controversial accord.

Sigmar Gabriel, also the vice chancellor, told the RND group of regional papers that his Social Democratic Party "doesn't wish to be part of a bad deal", as he warned against a hastily negotiated agreement on the so-called Transatlantic Trade and Investment Partnership (TTIP).

He said Merkel "was wrong to say, in the euphoria of (US President Barack) Obama's visit to Germany, that we will be able under all scenarios to conclude negotiations this year".

Washington and Brussels want the TTIP completed this year before Obama leaves office, but it has faced mounting opposition on both sides of the Atlantic.

Gabriel, whose party is the junior partner in Merkel's coalition government, already said earlier this month that the deal "will fail" if the United States refuses to make concessions.

Opinion polls show that people in the eurozone's biggest economy are growing increasingly wary of the proposed pact despite Merkel's continued support.

Some 70 percent of Germans polled this month said they believed the TTIP would bring "mostly disadvantages".

Tens of thousands of Germans have so far taken to the streets in protest against the treaty, including during last month's visit by Obama.

Meeting in Japan this week, leaders of the G7 nations -- the US, Germany, Japan, Britain, Italy, France and Canada -- expressed their support for a TTIP agreement this year, as long as it is "ambitious, comprehensive, high standard and mutually beneficial".

The next round of TTIP talks is set to take place in June.

The wide-ranging pact would create a free-trade zone covering 850 million people. Critics say it would come at the expense of jobs, consumers and the environment.