The Kremlin says the Russian leader has signed a law extending presidential terms from four to six years.

President Dmitry Medvedev's final endorsement of the legislation follows its quick approval by both houses of parliament as well as Russia's 83 provincial legislatures.

Critics have suggested the legislation was introduced by Medvedev in November before Prime Minister Vladimir Putin possibly seeks to return soon to the presidency.

Putin was constitutionally barred from seeking a third consecutive term. His protege Medvedev won the post in March by a landslide.