"More than 400 kilometers [of pipes] were laid by the end of 2018," Mueller said.
READ MORE: US Threatens Sanctions Against Nord Stream 2 Contractors — Reports
He noted that the company still planned to complete the construction of the pipeline by the end of 2019.
Nord Stream 2 is a joint venture of Russian gas giant Gazprom and five European companies. It aims to deliver 55 billion cubic meters (1.9 trillion cubic feet) of Russian natural gas annually to the European Union via the Baltic Sea and Germany.
The pipeline project has been welcomed by some countries in Europe and opposed by others that feel it might increase their dependence on Russian gas.