Russia's only major independent pollster, the Levada Centre, has been designated as a "foreign agent", the Russian Justice Ministry said today, two weeks ahead of nationwide parliamentary elections.

"The recognition of the organisation as a non-commercial body performing the functions of a foreign agent was established in an unscheduled document check," the Justice Ministry said in a statement. It did not give a reason for its decision.

Levada was not immediately available for comment.

Russia's main pro-Kremlin United Russia party is expected to comfortably win the elections on September 18, which are seen as a dry run for Vladimir Putin's presidential re-election campaign in 2018.

But battling a deepening recession and falling living standards, authorities have taken steps to subdue opposition voices and organisations, including election monitors, viewed as critical of the Kremlin.

The term "foreign agent" is part of a 2012 law governing groups which receive foreign funding and engage in political activity. It has previously been used to put pressure on organisations deemed "undesirable" in Russia.

Levada is the most respected of Russia's three main pollsters. While it routinely reports Putin's approval ratings in excess of 80 per cent, it is widely seen as more independent than its state-run competitors, VTsIOM and FOM.