Parties to the twin Nord Stream pipeline through the Baltic Sea are covered for plans to expand the existing infrastructure, Russia's Gazprom said.

Gazprom Chairman Alexei Miller last month signed a shareholder agreement on the development of the second phase of the twin Nord Stream pipeline system in the Baltic Sea with his 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 to the German coast, bringing the net aggregate annual capacity to 1.9 trillion cubic feet of natural gas.

Miller told an audience at an investment conference in St. Petersburg the expansion was not considered a brand new project.

"We have signed binding documents with the European partners," he said. "Technically it will be the same as the Nord Stream."

The project will be developed by a company named New European Pipeline, where Gazprom would hold a 51 percent share. European governments have expressed concerns about Gazprom's practices in the regional energy market, saying they're opposed to companies that control both transit arteries and reserves.

The European Commission ruled earlier this year that, "ultimately, each member state in the region should have access to at least three different sources of gas."

Fitch Ratings in September said funding and market challenges could get in the way of Nord Stream's expansion. Western sanctions and a weak energy price climate was hindering some of Gazprom's funding, the ratings agency said.