Vladimir Putin accepted the leadership of the dominant United Russia party, securing his grip on power after he leaves the Kremlin and becomes the prime minister next month.

"I'm ready to accept additional responsibility and to head United Russia."

Putin said at the party congress held across Red Square from the Kremlin on Tuesday that he was ready to accept the job.

Becoming head of United Russia enhances Putin's power base in the State Duma, the lower house of Russia's parliament, where the party holds a two-thirds majority.

Speaking before Putin, Dmitry Medvedev turned down an offer of membership in the party.

"I'm convinced that after my election as head of state it would be more correct to stay outside of one of the political parties."

Medvedev added he supported Putin in taking the party leadership, which both he and Putin said would improve coordination between the government and the parliament.