A top European Union official says the Nord Stream gas pipeline project that would deliver supplies direct to Germany from Russia appears to break EU rules.

European Council President Donald Tusk said on Friday that "Nord Stream does not help diversification, nor would it reduce our energy dependence."

But Tusk said the EU's executive Commission must conduct a legal and technical analysis of whether the Nord Stream 2 project would contravene any laws.

Speaking after hosting a summit of EU leaders, Tusk said they decided that any new energy infrastructure must help reduce energy dependency and diversify suppliers.

The EU depends on Russia for much of its gas needs, most of which goes through Ukraine. Gas price disputes between Russia and Ukraine have interrupted supplies to Europe in the past.