President Obama on Sunday began a two-day visit to Germany, where he will focus on trying to make progress on trade talks between the United States and Europe.

Speaking at a news conference in Hannover, Obama and German Chancellor Angela Merkel agreed the U.S. and European Union need to "keep moving forward" on negotiations for the Trans-Atlantic Trade and Investment Partnership, or TTIP.

Obama also said the U.S. and Germany are among each other's largest trade partners, and said "it is indisputable" that U.S. trade deals with other countries have strengthened the American economy.

While Merkel has shown support for the deal, Vice Chancellor and Economy Minister Sigmar Gabriel was quoted Sunday as telling the Handelsblatt newspaper that "the Americans want to stick to their 'buy American' idea. We can't accept that."
 
He also complained that the U.S. doesn't want to open public tenders to companies from Europe.

"If the Americans stick to this position, we don't need a free trade agreement. Then TTIP will fail," Gabriel said.

On Saturday, thousands swarmed the streets in Hannover to protest the agreement. In November, more than 100,000 protested the deal in Berlin. Proponents argue that it would boost business at a time of global economic uncertainty. Critics fear the erosion of consumer protections and environmental standards.

Negotiators want to finalize key parts of the deal before the year ends.

It's not certain that the next president would pick up where Obama leaves off on the trade deal. The pact has not been a top issue in the campaign to choose Obama's successor, but both leading candidates — Democrat Hillary Clinton and Republican Donald Trump — oppose a pending Asia-Pacific trade pact for its potential impact on American jobs and wages.

Although TTIP is the primary focus of Obama's visit, other issues  on the agenda include efforts to counter the Islamic State group, improve cooperation on counterterrorism and encourage countries to share law enforcement information.

Obama also wants to give a public show of support for Merkel's "courageous" handling of the migrant issue. Her decision to allow the resettlement in her country of thousands fleeing violence in Syria and other Mideast conflict zones created an angry domestic backlash. Merkel recently helped European countries reach a deal with Turkey to ease the flow, but she and the other leaders are now under pressure to revisit it.

Merkel and Obama are scheduled to open the city's annual industrial fair later Sunday, at which the United States is the featured country this year. Ahead of the press meeting, Merkel welcomed Obama with military honors.

The Associated Press contributed to this report.