Adding on to the Nord Stream natural gas pipeline running from Russia to European shores would impact the regional market significantly, an EU official said.

Russian energy company Gazprom in September signed shareholder agreements on the development of the second phase of the twin Nord Stream pipeline system with its counterparts at German energy companies BASF and E.ON, as well as those from French company ENGIE, Austria's OMV and Royal Dutch Shell.

Under the proposed expansion, two more lines would be added to the existing network running through the Baltic Sea to the German coast, roughly doubling the pipeline's net capacity.

The European Union has expressed concern about Russia's control over the regional market as the Russian gas company typically controls both the transit networks and the reserves they deliver.

Maros Sefcovic, a European leader on energy issues, told members of the European Parliament in Brussels concerns about the second phase of Nord Stream go beyond immediate regulatory matters.

"Nord Stream 2 could alter the landscape of the EU's gas market while not giving access to a new source of supply or a new supplier, and further increasing excess capacity from Russia to the EU," he said.

Gazprom said last year the expansion would not meet the regulatory conditions to be considered a new project. The second phase of Nord Stream would be developed by a company named New European Pipeline, and Gazprom would hold a 51 percent share.

In January, Ukrainian energy company Naftogaz, which has been under pressure from Gazprom to meet its contractual obligations, filed an official complaint in Europe, arguing Russian gas pipeline expansion plans would limit competition.

Russia meets about a quarter of European gas needs, though most of those reserves head through the Soviet-era pipeline network in Ukraine.

All networks, stressed Sefcovic, face the potential for disruption.