The European Commission said the deal would have hurt competition and led to higher prices for consumers, dismissing the companies' argument that it would help them better compete against Chinese rival CRRC.

Following the EU veto, German Economy Minister Peter Altmaier said that Europe should look at changing its rules to facilitate cross-border mergers and create European champions which can compete with rivals from China and the United States.

Altmaier launched a committee of antitrust experts last year to modernize German and European competition law with the goal of safeguarding Germany's competitiveness.

The committee has identified several themes to look into such as whether antitrust laws need to be amended to enable internationally competitive digital companies.

But the moves have concerned some and fears of being left behind China and the United States with their different antitrust frameworks should not drive the debate in Europe, Peter Alexiadis, a partner at Gibson Dunn said.

"The EU is a thought leader in antitrust, and has been for a number of years. There is no reason why it should not continue to do so, especially in combination with international fora such as the OECD. In a global marketplace, unilateralism will get us nowhere in the field of antitrust," he said.

Still, there is room for updating the rules, he said.

"We probably need to move away from the straightjacket of concerns about short term price rises and develop our views about an idea of consumer welfare that is more dynamic and more consistent with important emerging public policy values common across all EU Member State political cultures," Alexiadis said.

Another issue being looked at by the committee is whether the antitrust regime needs to allow for more innovation and investment in key technologies. The committee will also examine whether competition laws can be integrated with consumer protection and consumer protection laws.

The committee is due to present proposals later this year. Changes in EU merger rules need to be approved by all 28 EU countries and consent from European Parliament.

(Reporting by Andreas Rinke; Writing by Michelle Martin; Editing by Paul Carrel and Alexander Smith)

By Andreas Rinke and Foo Yun Chee