BERLIN (AP) — The European Union blocked the proposed merger of Germany's Deutsche Boerse and the London Stock Exchange on Wednesday, saying that it had "very serious" concerns about the deal's impact on competition.

The deal would have created "a de facto monopoly in the crucial area of fixed income instruments," such as bonds and repurchase agreements, EU antitrust chief Margrethe Vestager said.

The decision was expected after the London exchange said last month that it couldn't commit to selling its majority stake in the electronic bond market MTS, which would have alleviated the EU's concerns.

The deal would have combined Deutsche Boerse's Frankfurt-based clearing house, Eurex, with LSE's LCH.Clearnet and the Rome-based Cassa di Compensazione e Garanzia.

The companies announced the deal in March 2016, three months before British voters decided in a referendum to leave the European Union. Based on their stock market value at the time, the two companies together were worth about $30 billion.

Both companies had insisted that the deal made sense even in case of Brexit.

Brexit wasn't cited as a factor in Wednesday's decision, but the vote also complicated the deal's prospects as it called for the companies to be united under a U.K.-based holding company — an idea questioned by some in Germany in light of Britain's EU departure

Shareholders in Deutsche Boerse, which operates the Frankfurt stock exchange, would have owned 54.4 percent of the holding company.