Putin, president from 2000-2008 and now prime minister, is expected to easily recapture the presidency in an election in March.
But opinion polls indicate a parliamentary election to be held next week could loosen his United Russia party's domination of Russian politics.
Some speculators believe United Russia will lose its current two-thirds majority that has allowed it to change the constitution at will.
The timing of the announcement of his nomination for the presidency - which he said would seek in September - appeared aimed at giving United Russia a boost in the December 4 parliamentary vote amid flagging support. Read More