European stocks closed lower Thursday, after the U.S. said it would impose tariffs on steel and aluminum imports from the European Union, Canada and Mexico.

The pan-European Stoxx 600 shed gains from earlier in the session, closing provisionally down 0.63 percent, with most sectors in negative territory and major bourses mixed.

Germany's 30-stock DAX index was among the worst performing bourses in Europe, down 1.4 percent, amid growing fears of protectionism from the U.S. German magazine WirtschaftsWoche reported Thursday that President Donald Trump hopes to block the country's luxury carmakers from the U.S. market. Autos stocks fell on the news, with Porsche and Groupe PSA both dropping over 2 percent.

Spain's IBEX 35 index, meanwhile, was 1 percent lower, ahead of a no-confidence vote on Prime Minister Mariano Rajoy's leadership. If successful, the vote would topple the incumbent government and allow Spanish Socialist Workers' Party leader Pedro Sanchez to take the reins.

Europe's bank stocks were among the worst performers on Thursday, dragged down by Deutsche Bank. The German bank slumped to the bottom of the European benchmark after the Wall Street Journal reported that its U.S. business was designated by the Federal Reserve as being in "troubled condition." Shares were down by almost 7 percent.

Meanwhile, Irish building materials group CRH said Thursday that it would streamline some of its European and American businesses by merging them in an effort to boost profit margins. The company's stock was among the top performers in Europe, up 3.67 percent.