Vestager's news conference will start at 11 a.m CET (0900 GMT), the EU executive said in a statement on Tuesday, without providing further details.

Last week, sources told Reuters that Vestager would on Wednesday lay out the case for stopping the fifth attempt by the two companies to create Europe's biggest exchange.

The British government is also due to start launch its procedure for leaving the European Union on Wednesday.

Last month, LSE set the stage for a negative decision by the EU competition enforcer when it rejected a demand to sell its MTS Italian trading platform.

(Reporting by Foo Yun Chee; editing by Philip Blenkinsop)