German chancellor Angela Merkel has warned that the Nord Stream 2 gas pipeline project can only go ahead if Ukraine’s role as a transit country for Russian gas is protected.

Her remarks suggested a hardening of the German position in relation to the $11.7 billion infrastructure project, which aims to double the amount of gas Russia can deliver via the Baltic Sea to Germany. The 1,200-km pipeline will run from Vyborg in Russia to Lubmin in Germany, allowing Russian gas producer Gazprom to circumvent the more costly route through Ukraine.

The new pipeline has been criticized by eastern European countries, which fear that Nord Stream 2 would increase European dependence on Russian gas at a time when political tensions with Moscow are on the rise. Several countries—most notably Ukraine—also stand to lose lucrative transit fees.