MOSCOW, April 25 (RIA Novosti) - Russia's president signed changes to a law imposing restrictions on referendums, which critics say are a further Kremlin move to curb democracy in the country.

The amendments reduce the issues that can be put to a referendum, those that "run counter to the Constitution" and are "within the jurisdiction" of the president, government and parliament. These include budgetary issues.

The State Duma, lower house of parliament, approved the amendments proposed by the dominant, pro-Kremlin party United Russia, on April 4. The upper parliamentary house, the Federation Council, passed them on April 16.

Putin steps down in May after eight years in office to give way to his ally and preferred successor, Dmitry Medvedev. Putin stays as prime minister and will head United Russia, the country's largest party with a two third majority in the State Duma.

Putin has been criticized for a clampdown on democracy during his tenure, including by abolishing gubernatorial elections, pressurizing NGOs, and intimidating the opposition.

Western monitors criticized parliamentary and presidential elections in Russia last December and in March for not being free and fair.