Ukrainian President Viktor Yanukovych is using the 25th anniversary of the Chornobyl nuclear disaster to call for funding for a containment shell that would seal off the destroyed reactor.

"We have paid for the peace of the planet with the lives and health of thousands of compatriots," Yanukovych said Tuesday in a statement on his website renewing the call for funding. "No nation … can overcome the consequences of a catastrophe of such a scale by itself."

About $300 million is still needed for the new shelter.

Memorials for the accident began in Ukraine at 1:23 a.m. local time, the moment of the 1986 blast at the nuclear plant. 

In Kyiv, at a monument to firefighters and cleanup workers who died of radiation poisoning, priests sang hymns, people lit candles and a bell tolled 25 times to mark the passage of time.

"The world had not known a catastrophe in peaceful times that could be compared to what happened in Chornobyl," said Russian Orthodox Patriarch Kirill, who led the early morning service. "It's hard to say how this catastrophe would have ended if it hadn't been for the people, including those whose names we have just remembered in prayer."

Yanukovych attended a memorial service later in the day with Russian President Dmitry Medvedev.

Medvedev called on the international community Tuesday to take part in developing a set of rules for safer nuclear energy.

"The consequences of the accident have been huge, but if it hadn't been for the work of the 'liquidators,' the work of the firefighters, the rescuers and doctors, these consequences would have been global. We must remember that."

The Chornobyl accident released the radioactive equivalent of more than 400 times of that released by the atomic bomb dropped on Hiroshima in 1945.

With files from The Associated Press