Russia's ruling United Russia party is electing the newly appointed Prime Minister, and now former President, Dmitry Medvedev as party leader at a party congress on Saturday.

In late April, Medvedev, who was then head of state, agreed to lead the party and became a member on Tuesday. The incumbent president, Vladimir Putin, who presided over United Russia from 2008-2012, never formally joined the party.

The 13th congress of the United Russia party in Moscow will bring together 670 delegates and about 1,600 guests, including Serbia's president-elect Tomislav Nikolic and members of about 30 foreign delegations, RIA Novosti reported.

The agenda of the congress will also include the election of the party's main bodies, including the General Council and the Supreme Council, and the adoption of amendments to the party's charter.

On the eve of the congress, Medvedev proposed sweeping reforms within the party to make its work more efficient and transparent.

RIA Novosti points out that after dominating the political scene through the late 2000s, United Russia was faced with slipping popularity ahead of the State Duma elections in December 2011, in which it narrowly clutched a majority. The vote was marred by widespread fraud allegations, though most of them were not confirmed by the courts.

United Russia, slapped with the popular derogative slogan "the party of crooks and thieves" during the elections, was accused by critics of being ineffective and having no distinct political platform. Party bosses, including Medvedev, promised after the vote a radical revamp of United Russia, whose support rating stood at 50 percent in May, according to state-run pollster VTsIOM.

Meanwhile, the newly inaugurated new-old Russian President Vladimir Putin has named the new members of the Russian National Security Council, the Kremlin said on Saturday.

The council is a presidential consultative body that works out decisions on national security affairs. It is composed of key ministers and agency heads.

Putin appointed Prime Minister Dmitry Medvedev, Federal Security Council Chief Alexander Bortnikov, Presidential Administration head Sergei Ivanov, Interior Affairs Minister Vladimir Kolokoltsev, Foreign Minister Sergei Lavrov, Federation Council Speaker Valentina Matvienko, Duma Speaker Sergei Naryshkin, Russian Security Council Secretary Nikolai Patrushev and his deputy Rashid Nurgaliyev, Defense Minister Rashid Nurgaliyev, Foreign Intelligence (SVR) director Mikhail Fradkov and Boris Gryzlov new members of the council.