Chancellor Angela Merkel says it's in Germany's "national interest" for Britain to remain part of the European Union.

Merkel told parliament on Wednesday that Britain was a key ally of Germany on many issues and that she would do everything possible to ensure that the nation remained an "active member" of the trade bloc.

Merkel's comments came ahead of a two-day summit in Brussels where Britain's upcoming referendum on whether to stay in the EU is a major topic.