"The proposals will concern the responsibility of the countries using nuclear power, including the timeliness of measures in case of emergency," Medvedev said in a special address to mark the 25th anniversary of the world's worst nuclear accident at the Chernobyl nuclear power plant in the Soviet Union in 1986.

"Additional safety requirements are needed for the construction and use of nuclear facilities," he said.

The Russian president also called for greater transparency during nuclear emergencies.

Medvedev is visiting Chernobyl on Tuesday, along with a number of Ukrainian officials including President Viktor Yanukovych.

"Chernobyl became a lesson for all mankind and made us reconsider the safety and security of nuclear power generation," Russian Prime Minister Vladimir Putin said in a statement.

On April 26, 1986, an explosion at the No 4 reactor at the Chernobyl power plant sent a cloud of radiation over large areas of Europe. At least 30 people died in its immediate aftermath. More than 350,000 people were evacuated from contaminated areas.

A 30 kilometer exclusion zone remains in force around the plant.

"Today we mourn for those who died and lived through that tragedy," Medvedev said.

The anniversary comes amid the ongoing emergency at Japan's damaged Fukushima Daiichi nuclear plant following the March 11 earthquake and tsunami.

Ukraine, along with the European Union and the European Bank for Reconstruction and Development, is building a new shelter above the ruins of Chernobyl's No 4 reactor and the existing concrete and steel sarcophagus.

An international conference in Kiev last week raised 550 million euros of the 740 million euros needed to finance the new radiation shield.

Medvedev said Russia would allocate 45 million euros for the shield's construction in the next two years.