The head of the largest party in the European Parliament has launched a scathing attack on the $11bn Nord Stream 2 project to pipe more Russian gas into Germany.

Manfred Weber, chairman of the centre-right European People’s party, said the proposed pipeline would undermine the EU’s foreign and security goals by increasing dependence on Gazprom, Russia’s gas export monopoly.

“The EU risks creating detrimental consequences for the gas supply in central and eastern Europe, including Ukraine, in particular against the background of Gazprom’s announcement to stop gas delivery through Ukraine once Nord Stream 2 is finalised,” he wrote in a letter to Sigmar Gabriel, German economy minister, and Miguel Arias Cañete, EU energy commissioner.

One of the most sensitive political issues surrounding Nord Stream 2 is that its route under the Baltic Sea could divert some of the €2bn that Ukraine’s rickety economy derives from gas pipeline transit fees.

Mr Weber’s intervention is significant because he is a senior German politician whose party is allied to Chancellor Angela Merkel’s within the EPP. Germany is seen as the prime agitator in favour of Nord Stream 2, while Italy and Poland are bitterly opposed.