Russia-backed pipeline operators say the move is due to annual maintenance work. But German ministers believe the shutdown is politically motivated to put pressure on Berlin.

German Economy Minister Robert Habeck said last month that Russian President Vladimir Putin was using gas as a "weapon" in response to EU sanctions.

Russia's state-owned gas company, Gazprom, reduced in mid-June the flow of gas through Nord Stream 1 to only 40 percent of the pipeline's capacity. It blamed delays in returning equipment repaired by German energy company Siemens.

The Canadian government says it will now return an overhauled Siemens turbine to Germany for the pipeline. The move angered the Ukrainian government, which accused Canada of adjusting sanctions against Moscow "according to Russia's whims."